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-   -   How to Eco-drive the VW PD TDI Diesel (https://ecomodder.com/forum/showthread.php/how-eco-drive-vw-pd-tdi-diesel-38306.html)

COcyclist 04-16-2020 02:28 PM

How to Eco-drive the VW PD TDI Diesel
 
I am starting this thread to pass on my experience driving my TDI Golf. I am the second owner of this car and purchased it when it was new enough that people on TDIclub said you could not get good mileage in the PD engine. (This engine has the high pressure fuel injectors built into the top of the head and driven by the cam.) I did a lot of reading and started doing some mods and my mileage started to improve. One of the great things about the TDI is that you can drive it like you stole it and still get nearly 40 mpg. (see the lowest entry in my fuel log)

The first key to driving a diesel efficiently is to buy the right car for its intended use. Diesels are great highway cars. This engine is most efficient when it is fully warmed up and it uses very little fuel, even at idle, so it warms up quite slowly, especially compared to a gasoline/petrol engine. It is not the best choice for short trips running errands around town. Buy a used Leaf for that. (Or better yet a bicycle). If your regular commute has a lot of stop and go traffic or city driving a hybrid would be a better choice. If many of your trips can be an hour or more of open highway, you may love the TDI with a manual transmission. Mk IV automatics were not reliable, are heavier and less efficient.

Many of these tips will apply to the newer TDIs. These can be a relative bargain right now as "fixed" ones are showing up with extended factory warranties.

COcyclist 04-16-2020 02:52 PM

I will be double posting because the Ecomodder website will time out your token if you take too long typing. If you have not saved it, you will lose all your work. Also, I do not have a build thread so I will be mentioning some mods and how they relate to Eco-driving.

The first thing I did to improve mpg was to air up the tires. The original Goodyears are rated to 44 psi and I increased them to 50 psi. Later I backed off to 46 in the rears as they have less weight and forces acting on them. I am amazed how far this car coasts. Coast whenever it is practical. This is one of the easiest ways to improve your mpg.

The second thing that is a must is instrumentation. I purchased a ScanGuage II so I can monitor coolant temperatures, instant mpg, intake air temperatures and current and tank mpg. I wanted to be able to monitor engine temperature since I knew I would be blocking some of the radiator grill. VWs have a temperature guage in the dash but it is damped from the factory. In other words, it gets to normal and stays there. A ScanGuage or UltraGuage gives an accurate digital readout of engine temperature. This is vital to driving the TDI efficiently.

If you read about Hypermiling you may encounter some terms such as pulse and glide, DWL, EOC, DFCO and ICE-OFF. I will discuss these and how they relate to the TDI.

COcyclist 04-16-2020 04:42 PM

Pulse and Glide. As I stated in post #2 above- Coast when it is practical. If you are new to Ecomodder you may be amazed by the mpg numbers posted by some members on this site. Often the highest mileage is obtained by using Pulse and Glide. (Also know as EOC which stands for Engine-Off-Coasting.) Using this technique drivers accelerate to a target speed, say 60mph, and place the shifter in neutral and kill the engine. They coast or glide with the engine off to, say 50mph, and bump start the engine by putting it back in gear and letting out the clutch. This can be a way to get great numbers with a gasoline engine. DON'T DO THIS IN YOUR TDI! Ignore this at your own peril.

Here's why. #1- Diesel engines are very different from older gas/petrol engines. Gasoline engines have a throttle plate which does just what it sounds like it does. At part throttle it chokes off the intake air to maintain stochiometric ratio. This is good for combustion of gasoline but bad for low demand or idle fuel efficiency. In EOC Ecomodders install a kill switch near the shift lever to ground out the spark till the engine dies. They can glide with the engine off without turning the key. This avoids low load inefficiency and allows for glides using no fuel whatsoever. A diesel can burn at variable air/fuel ratios and are very efficient at idle. This means that there are much lower pumping losses at idle because there is no throttle plate and no vaccuum created and hardly any fuel is being injected. On my TDI I can coast (or glide) at 400mpg with the engine idling. There is no need to kill the engine to get good mpg numbers.

#2- Because the TDI shuts off the engine by not injecting fuel, it is much more complicated to kill the engine. I do not recommend using the key to do this. It not only shuts off the engine, it disables the airbags, vaccuum for power brakes goes down, no more power assist steering and it stops oil flow to the turbo. If your turbo has been running hard this is very bad! Don't do it.

COcyclist 04-16-2020 05:13 PM

E-On Coasting
 
In the TDI I use E-On Coasting because the Engine stays On and it seems to glide forever (for eons). Most of my trips are on 2 lane highways with other traffic so extreme Pulse and Glide would be rude at best and possibly dangerous with other cars around. I tend to drive at a steady state, usually a few mph below the posted speed limit if there are no other vehicles behind me. (Base Specific Fuel Consumption BSFC in this engine is around 1,800 rpm so driving closest to that rpm in 5th gear on flat roads is very efficient) However, I find I can get very good mpg numbers in rolling gentle hills and when coming into a town with lower speed limits by anticipating the road ahead and using an extended coast to the lower speed limits. If the road is wide open I will accelerate at the top of the hill and slip the gearshift into neutral and coast while getting between 350-400 mpg. This extends my coast times to at least 30 seconds or more which makes it more worthwhile.

DFCO- Deceleration Fuel Cut-Off. On the TDI the computer injects no fuel while engine braking. Mileage on the ScanGuage goes to 9999 or infinity. So why not do this all the time? The short answer is that it is going to slow the car down much faster than coasting in neutral. The trade off for using no fuel while engine braking is that you will use much more fuel in the long run, to get the car back up to speed. Should you use DFCO? Absolutely, but under the right circumstances. On long downhills where you would pick up too much speed? Yes! In fact I run the A/C full blast in the summer while engine braking to keep me cool and try to keep slowed down, or front and rear defrosters on high in winter. (Remember that part about diesels having no throttle plate? They don't engine brake the same as a gasoline engine. Now you know why semi trucks have a Jake Brake to create backpressure for engine braking) I use DFCO coming into stop signs and red lights. Otherwise, drive a little slower and coast, coast, coast on rolling terrain.

COcyclist 04-16-2020 05:39 PM

DWL Driving With Load
 
Some Ecomodders get good results with a gas/petrol engine by Driving With Load. You can use LOD on the Scanguage to monitor engine load and try to lock your foot in one position and drive with a constant load on the engine. This is sort of the opposite of what most cruise controls do. The factory cruise control will accelerate wildly uphill and at the crest go into engine braking. (Older gasoline engines do not have DFCO) This wastes fuel on the way up and kills your momentum, wasting fuel on the way down. In hills the use of cruise control is not the most efficient way to drive. DWL allows the driver to hypermile by anticipating the road ahead and allowing the car to slow somewhat on the way up and speed up (or E-On C) on the way down. In my experience with the TDI I have not seen significant mpg gains using DWL. The turbodiesel has tons of torque so even in a 1.9 4 cylinder most hills can be summited without a downshift. That said, it makes sense to use a modified version of this technique. If there are no other cars, I may slow slightly on the uphills if I anticipate that I will gain too much speed on the downhill. On rolling gentle hills I prefer to crest the hill at or slightly above the speed limit to extend my glide phase for as long as possible. This gives me better trip average mpg in my experience, and allows me to stay closer to the speed of other vehicles on the road. Here in the West the posted speed limit is 65 mph on rural highways but most of the traffic is driving 70 mph or higher.

COcyclist 04-16-2020 05:57 PM

DWB- Driving Without Brakes
 
Driving Without Brakes?:eek: There was a quote on this site a few years ago that said "If you are using your brakes you are doing it all wrong". Of course no one can drive without ever using the brakes and I want everyone to drive safely, first and foremost. The idea is to use the brakes sparingly. Someone here also said that when you use the brakes "you are turning fuel into brake dust". This means that if you come roaring into a stop you use heat friction to slow the car when you could have anticipated the stop and coasted and/or engine braked much sooner while using much less fuel. Therefore, roaring up to a stop wastes fuel. I have nearly 110,000 miles on my Golf and I am still on the original brake pads. They look nearly new and I live in the Rocky Mountains. Obviously I use the brakes as little as possible and I do not have to deal with stop and go traffic very often.

GreenTDI 04-19-2020 06:46 AM

Nice thread, COcyclist!

I also have some experience with TDI's. Learned to drive in a VW Transporter 2.5 TDI 5 cilinder, and now I have my own car with a 1.2 TDI 3 cilinder.

Big difference between the engines (big vs small) is that pulse and glide in the 2.5 TDI wasn't very effective, the engine had great breaking power because of internal friction, and coasting was possible but only at low speeds or steep descents because of the car's dramatic aerodynamic drag - it was a van.

The small TDI however has very little braking power. In fact, at small descents (2-3%) the car won't lose speed at all when releasing throttle. At decents of 5% and more it will even accelerate and I have to use the AC and/or downshift to generate more braking.

But I'm not using pulse and glide or coasting to get good mileage (yet).
On flat roads I will use cruise control and maintain steady speeds.
In hilly landschapes I'm never using cruise control, but I'm guided by the slopes and descents. So downhill I will gain some speed to maintain it below, and lose some speed going back uphill. For example, down the hill I'm speeding at 75 mph, and I'll reach the top at 55 mph. Always staying in highest gear, as you said, the TDI has a lot of torque and won't force you to downshift.

COcyclist 04-19-2020 07:55 PM

Quote:

Originally Posted by GreenTDI (Post 621971)
coasting was possible but only at low speeds or steep descents because of the car's dramatic aerodynamic drag - it was a van.

I agree. I have a Dodge Caravan and I just drove down a hill that I can coast for over a mile in the VW. In the van I had to drive down in gear and could only coast briefly in neutral on the steepest sections.

Instrumentation is helpful to learn the balance between coasting and using engine braking in the VW.

COcyclist 04-19-2020 08:12 PM

Using Cruise Control
 
As GreenTDI stated, cruise control can be very useful on flat roads. I find it can be a very good way to achieve higher mpg results under the right conditions. Ideally, cruise control will be used on straight flat roads with light traffic. You don't want to come speeding up onto slower traffic forcing you to kill momentum by braking. Also, even though the TDI gets great mileage at 50 mph you don't want to create traffic backups behind you and encourage drivers to take crazy chances to get around if the speed limit is 65 mph. Safety for all is more important than a few mpg for a Hypermiler.

ptitviet 04-20-2020 05:17 AM

Yup happy to share my observations (with my '15 Octavia 3 1.6TDI Greenline Combi). I do not use pulse and glide a lot on my car, as it tends to be less useful when the engine is not too powerful (my former car was a 265hp Renault Megane RS and I could get almost 2l/100km less by using pulse and glide). I only do hill pulse and glide by pulsing up and gliding down. When coasting I switch AC off as it the engine is less efficient when idling.

No mods on my car, only folding passenger mirror on long highway trips (0.1l/100km better). I only use ECO official tyre pressure, as I live in the mountain and want to keep the best handling possible. And when on eco mode, I drive only 100/110km/h on highway instead of 120/130 (Switzerland/France speed limits).

Until now I have owned the car one winter and got 48mpg (4.9l/100km) which is not bad with short trips uphill to the ski resorts and winter tyres. I am hoping to meet 3l/100km mark this summer with long holiday trips on secondary roads (80-90km/h). With winter tyres and longer trips (30km) I can already get about 4L/100km (58mpg), thanks also to the very good aerodynamics (0.59m2 measured by me thanks to Matlab).

I'd be happy to try front grille cover, but I am not very good with my hands and do not want to put something with no good finish on the car.

GreenTDI 04-20-2020 05:43 AM

Accelerating with the TDI:
Always depending on size of the engine. A decent 4, or large 5 or 6 cilinder will need less revs. But with every turbo charged engine, to little revs are as bad as too much.
For me - the little TDI - It's pointless to rev it under 1.500 rpm during accelerating. There is no turbo pressure underneath and accelerating will take too much time. The most economic way to accelerate with a small TDI: give enough throttle -> 3/4 is ideal. Never pedal to he metal, only if it's really necessary. Rev it up quickly to 2.200 rpm and upshift. Reving it above 2.500 rpm - in normal circumstances - is pointless. The 'cheapest', most effective power is concentrated between 1.500 - 2.500 rpm.

Once at speed:
It is possible to maintain very low speed in highest gear (less than 1500 rpm or under 50 mph), but when you need to accelerate again, you'll give the engine a hard time. Also taking into account of the size of your engine, a smaller engine will love some higher revs. Due to the extended 4th and 5th gear with recent cars, it turned out better to downshift from 5th to 4th when the speed drops under 45 MPH and to maintain it in 4th gear. It shows no difference in consumption on the on-board computer compared to the highest gear.

GreenTDI 04-20-2020 05:47 AM

Quote:

Originally Posted by COcyclist (Post 622004)
Safety for all is more important than a few mpg for a Hypermiler.

Indeed, completely my opinion. The MPG you'll win by driving very slowly, will be lost exponentially by all those non-hypermilers who have to brake because of you.

COcyclist 04-20-2020 12:49 PM

Quote:

Originally Posted by ptitviet (Post 622034)
Yup happy to share my observations (with my '15 Octavia 3 1.6TDI Greenline Combi). I do not use pulse and glide a lot on my car, as it tends to be less useful when the engine is not too powerful (my former car was a 265hp Renault Megane RS and I could get almost 2l/100km less by using pulse and glide). I only do hill pulse and glide by pulsing up and gliding down. When coasting I switch AC off as it the engine is less efficient when idling.

No mods on my car, only folding passenger mirror on long highway trips.

Until now I have owned the car one winter and got 48mpg (4.9l/100km) which is not bad with short trips uphill to the ski resorts and winter tyres. I am hoping to meet 3l/100km mark this summer with long holiday trips on secondary roads (80-90km/h). With winter tyres and longer trips (30km) I can already get about 4L/100km (58mpg), thanks also to the very good aerodynamics (0.59m2 measured by me thanks to Matlab).

I'd be happy to try front grille cover, but I am not very good with my hands and do not want to put something with no good finish on the car.

In post #4 I stated that I will run the A/C full blast on a 7 mile downhill near me to increase engine braking effect (or heat and wipers and rear window defroster in winter). When I am E-On coasting the A/C and all accessories except the radio are off to reach the highest mpg during the glide phase.

It looks like you are already getting great mpg in your Octavia. I believe it is similar to the Golf AllTrak that we can get here in the States. I used foam pipe insulation (it can be purchased in black) and pushed it between the grill bars on my Golf. I think it looks pretty stealthy and is easily removed if needed.

I fold my driver’s side mirror on the highway and removed the passenger mirror completely. I have small convex mirrors on each side but do head checks too.

COcyclist 04-20-2020 01:21 PM

Drive with a Hot Engine
 
Diesel engines are most efficient when fully warmed up and fed lots of cool air for combustion. Gasoline/petrol engines also perform better when warmed up but intake air differs in a Diesel. Many Ecomodders driving gasoline engines report much better mpg by using a “warm air intake”. They reroute the intake plumbing to pick up air from near the exhaust manifold so that it is warm coming into the engine. This may reduce peak power but they do most of their driving under low load/part throttle conditions. The throttle plate is mostly closed, the engine is working against high vaccuum, it is not running in its most efficient range. Warmer air is less dense so the throttle can be opened further for the same speed and they have lower pumping losses.

Diesels like lots of cool clean air. Since they don’t have a traditional throttle plate they can ingest lots of air and run very lean, using very little fuel, without creating vacuum. (The vacuum for the power brakes is from a vacuum pump driven by the camshaft). There is no need to route intake air from the exhaust manifold except perhaps to speed warmup. The downside is that extra oxygen can lead to higher NOX emissions so newer diesels have employed lots of technology to lower NOX emissions (and unfortunately reducing efficiency at the same time).

In general, DO NOT modify the intake for warm air in a diesel. Give it plenty of cool high pressure air from the front of the car (stagnation point). There are some intelligent tuners that sell smart tunes to decrease the demand for EGR that help the diesel run more powerfully, cleaner engines with less carbon buildup and return better mpg if that is your priority. Off-road or track use only of course. :rolleyes:

ptitviet 04-21-2020 05:46 AM

Hello!

The Greenline is not like a Golf Alltrak. Green stands for ecological. It is a special version already biased toward mpg :
- small 1.6 TDI 110hp engin
- very long ratio 6 gear manual gearbox (130km/h-85mph is 2000rpm)
- lighter with fewer equipments
- ride height lower -15mm
- various aerodynamic tweaks
- small wheels

I won't modify anything on the engine we don't have the same possibilities to tweak our cars in Europe than in the USA.

Seems we have otherwise quite the same receipt. I will do coasting down test once I get my new grille block and summer tyres to see changes in SCd and Crr.

GreenTDI 04-21-2020 06:24 AM

Quote:

Originally Posted by ptitviet (Post 622111)

I won't modify anything on the engine we don't have the same possibilities to tweak our cars in Europe than in the USA.

Chiptuning could help reduce consumption with about 5%. Only if you don't make advantage of the extra power, that is. You could save even more if the EGR has been closed and the particulate filter has been deleted. But those things are not recommended (emission-wise)!

COcyclist 04-24-2020 06:57 PM

Quote:

Originally Posted by GreenTDI (Post 622112)
Chiptuning could help reduce consumption with about 5%. Only if you don't make advantage of the extra power, that is. You could save even more if the EGR has been closed and the particulate filter has been deleted. But those things are not recommended (emission-wise)!

Of course mine is old enough that it did not come with a particulate filter. I did remove the muffler and replaced it with a straight pipe. It is not loud. The turbo and catalytic converter seem to muffle exhaust noise just fine.

COcyclist 04-24-2020 07:46 PM

Help your engine warm up quicker
 
The PD TDI has 3 extra glow plugs in the coolant at the top of the engine. This was done by VW to speed warmup and give some heat for defrost and cabin heating during cold starts in winter. That is a large current draw on the alternator until the engine reaches 150 degrees F when the computer shuts them off. This is yet another reason why your TDI gets poorer mpg when it is cold. For optimum mpg you want to do everything you can to help it reach full temperature as soon as possible.

What to do? Here is a partial list:

Park in a heated or insulated garage.

Install a tank type coolant heater. Google FrostHeater on TDIclub. This allows me to plug in a couple of hours before I drive and puts heat in the head for easier starts, and coolant so defrost works better. I highly recommend this mod. I use before I drive even in summer. It really helps the poor engine start better if you have to park outside at 20 below zero like I did this last winter.

Put a small electric space heater in the cabin for a few minutes in winter. I have one with a tip over protection that I put on the driver's side floor. 15 minutes takes the chill off the entire cabin. You can allow the engine to fully warm before calling for cabin heat from the engine.

Grill blocking. I use black foam to block the upper grill year round and put a hard cover over that in winter (partly to protect from rock chips).

Katz stick-on electric heater on the oil pan. This warms the oil and the bottom of the engine. Surprisingly, this heats the whole engine compartment more than the tank heater.

Make sure your noise panel is in place and intact. The VW comes with a partial "belly pan" under the engine. It is molded plastic and easily damaged or sometimes mechanics remove it for engine service and it is not replaced. This allows lots of cold air into the engine compartment and hurts aerodynamics. I have installed a Panzer Plate made from 1/4" aluminum and still have the noise panel next to the engine. It took a little trimming but I feel it insulates better than just the aluminum.

I may add more if I think of something.

I almost forgot. In addition to all of the above, do a few pulls with boost to get some combustion heat into the engine and coolant loop. This is one time where it makes sense to do some medium hard accelerations to get to 150 degrees and get better mpg.

COcyclist 04-24-2020 08:03 PM

I hope this is still useful
 
I just noticed as of today this post has 295 views. I suppose I should have posted this years ago, but I seem to have the time now.

Although my timing is all off. We are in a world pandemic so people are hardly driving. Russia and OPEC are in a price war. Oil futures traded at less than zero dollars per barrel. Gasoline was being sold outside Denver for $.99/gallon while diesel was still $2.20/gallon. Tighter emissions regulations and Dieselgate have essentially killed off the small diesel in the US. There is not much incentive to buy a diesel now in the US. We don't get the Greenline versions that are available in Europe and gasoline engine cars are getting much better mileage with direct injection, CVT and multispeed transmissions. Electric cars are becoming more widespread.

Perhaps those of us who are fans of the diesel get it and will be able to keep our cars for a long time and enjoy the driving experience while getting great mpg in these cars.

GreenTDI 04-25-2020 06:05 AM

The positive effect of dieselgate is that new EU6 diesel engines (most recent emission standard) are even cleaner than modern gasolines. But the technology has made them more expensive in purchase as in maintainance and no longer profitable for individuals. Not to mention the higher tax worldwide due to the diesel scandal. To break-even with a gasoline car you should drive at least 22K miles a year and that's a lot.

But I don't believe diesel (or combustion engines in general) will disappear soon. There is still great demand here in Europe. And for those who have to pull loads, there is no equivalent alternative yet. Small low duty diesels however will become (worthless) museum pieces.

MeteorGray 04-26-2020 01:18 PM

Yeah, the Germans knew how to make diesels make emissions. It's just that the VW group wanted to beat the world at it, even if they had to lie, cheat and steal to do it.

Unfortunately, they only managed to destroy shareholder value and, ironically, cripple the future of diesel cars in the process.

GreenTDI 05-07-2020 05:55 AM

Quote:

Originally Posted by MeteorGray (Post 622478)
It's just that the VW group wanted to beat the world at it, even if they had to lie, cheat and steal to do it.

Believe me, they were not the only car manufacturer …

But nevertheless, they build some iconic diesel engines in the present past. It all started with naturally aspirated engines in the early 70's. VW took her 1471 cc gasoline engine and simply converted into a diesel engine. The first Golf diesel was born. Besides turbo charged diesel engines, VW made naturally aspirated ones until 2008.

The most iconic TDI's are:

Distribution injection pump
1989: 2.5 TDI: 5 cylinder with 118 hp and 200 lb.ft of torque. It gave the Audi 100 a top speed of 125 MPH and an average consumption of 40 MPG.
1991: 1.9 TDI: 4 cylinder with 89 hp and 140 lb.ft. The beginning of a succesfull 20-year carreer.

High pressure fuel injector
1998: 1.9 TDI: the new technology reduces consumption phenomally. The 1.4 TDI 3 cylinder was a derivative of that one and became the first Bluemotion engine. With power outputs from 69 hp to a massive 157 hp and 243 lb.ft they left all competitor behind in terms of power, consumption and reliability.
1999 1.2 TDI: most popular 3 cylinder diesel engine. Very progressive economy wonder for that time. Especially in the futuristic Audi A2 made of aluminum. They claimed 117 MPG.
2002: 5.0 TDI: a massive 10 cylinder engine with outputs from 300 to 350 hp and an incredible 627 ft.lb of torque. This thing is truck worthy and it is found in the upper class cars like the Touareg, Pheaton
-> The largest TDI however was a 6.0 V12, only for the exclusive Audi Q7, producing an overwhelming 500 hp and 737 ft.lb.

Common Rail
2009: 1.6 TDI: new 4 cylinder engine which formed the basis for the 0.8 TDI 2-cylinder (VW XL1) and the 1.2 TDI 3-cylinder (VW Polo Bluemotion) with power outputs from 47 hp to 118 hp and a consumption up to 230 MPG for the aerodynamic XL1.
2020 2.0 TDI evo:: perhaps the last diesel engine from VW. Always in combination with a 48-volt mild hybrid system. The exhaust gas of this engine should be purer than city air.

And to remain relevant to the topic: they all need a different style of driving, especially between the different injection techniques :D

COcyclist 05-19-2020 06:13 PM

Only drive your TDI in summer
 
To achieve the best mpg there are a host of reasons why winter driving is not your friend. We discussed several reasons why a fully warmed Diesel engine is much more efficient in a previous post.

1. If you must park in sub-freezing temperatures your engine, transmission and the whole drivetrain will be cold and inefficient. Park in a heated garage if possible.

2. Cold air is more dense. It is harder to push the car through denser air.

3. Daylight hours are shorter. You may spend more hours with the headlights on. (and wipers, front and rear defrosters, the heater fan has a large current draw and in some cars heated seats-not mine). Powering the alternator to supply all these accessories hurts mpg.

4. Snow tires. In another thread I was testing smooth wheel covers for mpg and changed from winter tires to summer tires on alloy rims as part of the testing. Tire and wheel weight, tread pattern and perhaps rubber compound killed mpg. Changing to summer tires gave much better mileage change than any wheel cover change I tested.

5. Winter blend fuels may affect mpg. I do not have hard data on this.

6. Even modern diesels start harder in sub-zero temperatures. On a ski trip this past winter I had to park outside a condo for a couple of days in very cold temperatures without being able to plug in my engine heater. I needed to move the car so I attempted to start it one afternoon. It took multiple tries but it finally started reluctantly and I left it running for a while to recharge the battery and warm the engine somewhat. Idling a cold engine is certainly not good for mpg.

7. Diesel engines do not “warm up” while idling like a gasoline engine does. With no throttle plate the engine is drawing in the same amount of frigid air as the same size gasoline engine would at wide open throttle, while injecting very little fuel. Drive gently and even climb a hill if you need to get heat into the cabin.

COcyclist 05-19-2020 06:34 PM

Quote:

Originally Posted by GreenTDI (Post 622035)
The most economic way to accelerate with a small TDI: give enough throttle -> 3/4 is ideal. Never pedal to he metal, only if it's really necessary. Rev it up quickly to 2.200 rpm and upshift. Reving it above 2.500 rpm - in normal circumstances - is pointless. The 'cheapest', most effective power is concentrated between 1.500 - 2.500 rpm.

I agree except for “Never pedal to the metal”. I occasionally do a full throttle blast in 4th or 5th to keep the turbo linkages from getting sticky and to blow the accumulated oil out to the intercooler. In my car with no DPF you can see the cloud of soot behind me in the rear view mirror. Once it is cleared out, it runs clean even on subsequent hard pulls. I’m sure full throttle pulls are not helping mileage at that time but it “feels” like the car runs better afterward.

cRiPpLe_rOoStEr 05-20-2020 01:54 AM

Quote:

Originally Posted by COcyclist (Post 624635)
Diesel engines do not “warm up” while idling like a gasoline engine does. With no throttle plate the engine is drawing in the same amount of frigid air as the same size gasoline engine would at wide open throttle, while injecting very little fuel.

Some modern ones now feature a throttle-plate, even though it's for emissions compliance instead of cold-start concerns. On a sidenote, fitting an extra glowplug to the intake elbow of some older engines is also not unheard of.


Quote:

Drive gently and even climb a hill if you need to get heat into the cabin.
Got me to remember the day a friend who was not so used to Diesel engines told me quite surprised about a bus driver who kept flooring the throttle pedal right after a cold start in order to raise the temperature quicker.

GreenTDI 05-20-2020 09:37 AM

Quote:

Originally Posted by COcyclist (Post 624636)
I agree except for “Never pedal to the metal”. I occasionally do a full throttle blast in 4th or 5th to keep the turbo linkages from getting sticky and to blow the accumulated oil out to the intercooler.

True. It is better to prevent this internal pollution. Small distances are therefore also the big enemy of a diesel. I was only referring to the fact that it bad for the actual mileage, which collapses immediately.

Once every year I have the opportunity to sin on the Autobahn (sorry ecomodders, it feels like a confession)! by flooring (pushing it trough the floor) the car for at least an hour. :eek: The weeks that follow I clearly notice the difference due to a quieter running of the engine and indeed lower consumption.

cRiPpLe_rOoStEr 05-21-2020 08:43 PM

Quote:

Originally Posted by GreenTDI (Post 624681)
Once every year I have the opportunity to sin on the Autobahn (sorry ecomodders, it feels like a confession)! by flooring (pushing it trough the floor) the car for at least an hour. :eek: The weeks that follow I clearly notice the difference due to a quieter running of the engine and indeed lower consumption.

Passive regeneration of the DPF is not bad at all. Well, besides the increased fuel consumption which would involve an active DPF regeneration, with all the environmental concerns surrounding the higher amount of fuel required, even if the ECM sets a leaner AFR in order to raise the EGTs and as a consequence the NOx emissions increase a bit, that ends up being not so awful at all.

GreenTDI 05-22-2020 05:35 AM

@ cRiPpLe_rOoStEr

Indeed. Besides, it's nothing spectacular either: it feels like cruising around 110 mph at a comfortable 3.500 rpm still averaging 30 MPG. With a gasoline engine you see some other figures ...

So from time to time it is good to make the TDI work harder. Do it only with a warm engine and preferably in the middle of a long ride. This way you still have enough time to compensate for that extra consumption.

cRiPpLe_rOoStEr 05-22-2020 08:02 PM

Quote:

Originally Posted by GreenTDI (Post 624823)
Do it only with a warm engine and preferably in the middle of a long ride. This way you still have enough time to compensate for that extra consumption.

Sure. On a sidenote, makes me wonder how water injection would affect both the particulate matter buildup and the regeneration process.

mwebb 05-23-2020 06:57 PM

thermal shock
 
Quote:

Originally Posted by cRiPpLe_rOoStEr (Post 624878)
Sure. On a sidenote, makes me wonder how water injection would affect both the particulate matter buildup and the regeneration process.

watch out for thermal shock
on early VWs of the mark 4 vintage the heater on the AFR or 02 sensor does not get switched to on
until
after
the car gets to 50mph or thereabouts AND coolant temp crosses a threshold the value of which is not released to the mortals
to
avoid
thermal shock of the thimbles in the AFR / 02 sensors
on the theory that there will be no liquid h2o in the exhaust stream , it will all be in vapor state due to the heat / temperature in the exhaust

you do not want to crack the substrate in the DPF or the thimbles in the lambda sensors

so
no
you should NOT use water injection in any TDi or ever

imho

and
EGR is good
more EGR is better than less to a point and defeating a properly function ing EGR does not improve fuel economy or power as
EGR does not operate at high load anyway .

carbon buildup is mostly caused by the driver AND bad fuel
also
imho

current VW diesel tech
the opinions expressed are my own

i own 2 mark 4 golfs with BEW and 5sp
average hi 40s on both
less in colder weather
43psi on tire pressure
one has 225 45 17 continental tires
the other 205 55 16 michellin tires

cRiPpLe_rOoStEr 05-24-2020 01:04 AM

Quote:

Originally Posted by mwebb (Post 624941)
watch out for thermal shock

This is not a major issue at all. A properly-dimensioned water injection is just like some sort of "chemical intercooler".


Quote:

on the theory that there will be no liquid h2o in the exhaust stream , it will all be in vapor state due to the heat / temperature in the exhaust
It vaporizes while it absorbs latent heat from the intake air. When some alcohol is added to the water, usually methanol but it could also be ethanol (even the good old Everclear may serve as it's quite similar to the E96h used as a motor fuel in my country), it vaporizes quicker.


Quote:

you do not want to crack the substrate in the DPF or the thimbles in the lambda sensors
Water injection won't lead to a risk of cracking the DPF core or the lambda sensors. Otherwise, it would already be an issue to drive on a rainy day, which does a roughly similar effect to water injection.


Quote:

EGR is good
more EGR is better than less to a point and defeating a properly function ing EGR does not improve fuel economy or power as
EGR does not operate at high load anyway .
EGR may have some benefits under certain conditions, but it doesn't prevent water injection to fare better on other conditions. By the way, while EGR has been pointed out to increase particulate matter emissions, water injection can decrease both NOx and particulate matter simultaneously.

COcyclist 05-24-2020 10:29 AM

Quote:

Originally Posted by mwebb (Post 624941)
EGR is good
more EGR is better than less to a point and defeating a properly function ing EGR does not improve fuel economy or power as
EGR does not operate at high load anyway .

carbon buildup is mostly caused by the driver and bad gas

This has not been my experience and is counter to everything I have read about making Diesel engines run better (although perhaps with higher emissions).

This thread is about driving for mpg which means long periods of low load. This is the type of condition that caused carbon buildup for me in the past. After the tune, which defeats EGR after warmup, my Italian tuneups to blow out carbon are needed much less frequently and show much less carbon when I do.

Also, remember Dieselgate? The cars that VW allowed to cheat the US EPA test performed worse in power and mpg after the VW fix. They cleaned up emissions by calling for more high pressure and low pressure EGR. We had an A3 TDI “Clean Diesel” in the fleet. Even in the factory cheat tune it never came close to the mpg I could get out of the PD TDI.

There is one instance where EGR may help mpg and that is during cold starts. My friend has an 02 TDI and did an EGR delete. This removed the EGR cooler so the exhaust gas no longer warms the coolant on startup. It takes time and a few hard pulls before he gets much cabin heat. FWIW I did not remove the EGR cooler in my TDI for that reason.

mwebb 05-24-2020 11:31 PM

result in catastrophic failure
 
" .... This is not a major issue at all. A properly-dimensioned water injection is just like some sort of "chemical intercooler". ..... "

maybe
how ever
an IMproperly designed water injection system can be an engine killer

( many / most of the discussions regarding water injection on these very pages in this very forum would be
IMproperly designed for varying reasons. imho
and would ultimately result in catastrophic failure )

and
a lambda sensor killer
and
a DPF killer

so i would say it can be a very major issue NOT to be attempted by someone UNwilling to add those UNimprovments to his or her car , during the course of the experiment

we all pick our own paths , and , we are liable for our own actions when we pick the wrong path

mwebb 05-24-2020 11:44 PM

EGR is good , more is better , to a point , FREDs fuel is bad
 
....
This thread is about driving for mpg which means long periods of low load. This is the type of condition that caused carbon buildup for me in the past. After the tune, which defeats EGR after warmup, my Italian tuneups to blow out carbon are needed much less frequently and show much less carbon when I do. .....


right
EGR does improve fuel economy by displacing combustion chamber volume with an INert gas (exhaust gas with no or very little 02) that does not support combustion
so EGR makes the engine smaller at cruise AND reduces NOX by reducing combustion pressure wich in turn reduces combustion temperature so it is not as easy for N to combine with 02 to form NOX as that takes place mostly above 2500f .

less combustion chamber volume = less fuel consumed as fuel rate is determined by MAF flow on the mk4 system (primarily) . and MAF can not measure EGR flow so only counts the fresh air charge coming in .

poor quality fuel does not completely combust so it leaves carbon deposits
which decrease flow in the intake add turbulence to flow and INcrease compression ratio & screw up the swirl in the combustion chamber
none
of
those
things
are an improvement in Fuel Economy

EGR is good
carbon deposits from FREDs fuel is bad

MeteorGray 05-25-2020 09:19 AM

A good water injection system will keep combustion chambers clean of carbon. Such systems are useful for keeping exhaust gas temperatures at safe levels under heavy loads.

Piotrsko 05-25-2020 09:57 AM

Depending on where you water inject. In mine I fear water since it tends to park in the intercooler, make indegestible mayonnaise, and bend #3 rod.

COcyclist 05-25-2020 10:28 AM

Driving without A/C
 
We are entering summer here in the northern hemisphere. This may be a good time to talk about limited use of A/C for increased mpg. In short, the energy to run the compressor and fans comes from the engine. If you run the A/C a lot your mpg will suffer. What can you do so you don’t suffer from heat in the cabin? In no particular order...

1. Park in a garage or carport if possible so your car is not roasting when you enter it to start your trip.

2. Tint as much of the windows as is legal in your area.

3. If you must park in the sun, use a high quality sunshade in the windshield. A couple of US accessory manufacturers make some that are custom fit to the specific car. You could go a step further and make side and rear insulating shades. I did this on my little camper van and it makes a huge difference. There are plenty of how-to videos on YouTube.

4. When you return to a hot car, use the key in the driver door to hold “unlock” for 5 seconds to roll down all the electric windows at once, to let built up heat out before you drive (if it is hotter inside than out). In town at slow speeds where aerodynamic drag is lower, drive with the windows down for maximum ventilation.

5. On the highway there is a huge drag penalty to driving with the windows down. Roll up windows and use the fresh air vents directed on the parts of your body you want to cool. If you are driving solo, close off or redirect vents on the passenger side. If it is really warm I will open a passenger side window slightly to increase flow through the cabin.

6. Dress in the lightest clothing you can. On the hottest days I wear shorts and flip flops with a thin synthetic wicking shirt in light colors.

7. Prepare “cooling towels” pre-soaked in a small cooler so you can change them out as they warm up and dry out. I drape these around my neck and shoulders to extend my comfort range. I have also experimented with a chiller designed to reduce swelling after an injury. It circulates ice water through a pad that I place between my shoulder blades. I run it on a small inverter plugged into a lighter socket. It works great but requires more preparation than the cooling towels.

If you have passengers it may be better to run the A/C on “recirc” so you are not pulling in hot outside air. I rationalize that my per passenger mpg goes to 100 mpg, using only slightly more fuel to transport twice the cargo. My spouse is unwilling to do the silly hypermiling tricks when it comes to comfort.

8. If you must do extended engine braking on long hills, by all means run the A/C on high to help slow the car. Diesels do not engine brake like gas cars so I take advantage of some extra chilling at no mpg penalty while in DFCO.

cRiPpLe_rOoStEr 05-25-2020 11:47 PM

Quote:

Originally Posted by Piotrsko (Post 625019)
Depending on where you water inject. In mine I fear water since it tends to park in the intercooler, make indegestible mayonnaise, and bend #3 rod.

That's why an intercooler bypass for cold-starting and fitting the water injection nozzle after the intercooler are good measures to ensure safety.

COcyclist 06-29-2020 09:54 PM

I had the “opportunity” to be a courier for some medical supplies last week on some of Colorado’s great two lane paved mountain roads in the Golf TDI. I was reminded of a couple more tips for mpg. FWIW I averaged 50 mpg with spirited driving and some use of A/C and even a short construction zone on the interstate segment.

We have discussed DFCO and engine braking in previous posts and I was doing a lot of that. I also was trying to conserve momentum through the corners so I would have less acceleration losses coming out of the corners. I am running stock tires. One of the 4 is the original spare from the trunk. When the original Goodyears wore out I only bought 3 and mounted the spare from the trunk on one of my alloy rims. I changed the original shocks to Koni Reds with the front struts one click out from full soft. It firmed up the ride a little but really helped in the handling department. A very worthwhile upgrade in my opinion. Carry momentum as much as you can do safely.

While we are on the subject, weight reduction helps in handling, braking and acceleration, and generally improves mpg. I have removed the rear seat and replaced it with a lightweight flake board flat shelf. I carry my bicycle or skis inside instead of outside on a rack. I took out the spare tire and kept the jack and a can of tire inflator, which I have still never needed. I replaced the muffler with a straight pipe (don’t worry, the catalytic is intact). Total weight removed is about 100 lbs. Most of that coming from the seat back and the spare.

The TDI with a manual can be a fun, sporty car and still return much better than average mpg.

COcyclist 06-29-2020 10:25 PM

I have a couple more tips, some obvious and one debatable one.

1. Never put roof racks on your car (unless you have to). The roof of the car is in some of the fastest air flow and adding a roof rack adds to frontal area and disrupts what should be an area of attached flow. Putting bikes up there just makes it worse. Some people leave cargo boxes on the roof racks or even deflectors to get rid of the wind noise. The wind noise is turbulence and drag making its presence known. Take them all off!

If you have to pick up some lumber or carry a ladder across town, roof racks make a lot of sense, just remove them when you are done.

2. Carrying a bike on a rear bike racks add drag. I will add a rear rack if I am meeting a friend to go biking but I drive to his house with my bike inside.

Now the debatable one...

3. Get a trailer hitch? I have a small receiver hitch that I mostly use for a 2 bike rack. The rack folds compactly when not in use but can carry a bike for myself and a passenger. Back to the double the per passenger mpg argument. Effective per person 100 mpg.


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