Starting and stopping diesel engines.
 

I refuse to do the pulse and glide so I'm not talking about that but say in stopped traffic or every morning when I get to work I gotta stop get out walk over to a button hit it and wait for it to open. Is it worth it to kill the engine for a minute? I have always heard not to start and stop diesel engines and to leave them running instead of turning off for 1-8mins. Truth behind it?

What do you drive? I've read that it's good to let the engine run while the turbo cools before shutting down, so I would leave it running. I would imagine it's harder on turbos, fuel pumps, and starter motors to have excessive starting and stopping, so I would avoid it. Maybe I would consider killing the motor if I knew there would be more than 3min of idling.

..."tradition" has it that turbocharged diesels are better left ON rather than continuously being stopped & started.

It's a 2012 jetta tdi. Yea I'm just gonna leave it running from now on not to mention I hear diesel starters are EXPENSIVE.

Yes, traditionally diesels are supposed to be left idling.
Not anymore. Treat your diesel like a gas engine. The starter won't care. The turbo won't care. Excessive idling isn't good for modern aftertreatment systems anyway.

I don't do "engine off", ever.

Depends on your turbo lubrication. The diesel engine part won't mind. The finicky turbo (especially if it's a variable geometry one) will mind if it's oil-fed... and variable geometry turbos almost always use oil as part of the system that works the vanes (can't recall one that doesn't).

Probably not a big deal if you don't run hard enough to get it hot... but I've seen turbo failures on these "modern" diesels from owners who don't understand the peculiarities of the system.

Most VGTs (if not all) have engine coolant keeping them cool, so idling to "cool them" off really does nothing but waste fuel.

Yet another prime example of an old time habit that won't die. :rolleyes:

Sure, if you have just parked your semi hauling 50,000 lbs across the mountains, that engine has been working very hard and a cool down period is advisable. Likewise if you have just plowed 50 acres with your Steiger. Likewise if you have just pitted from going 180mph in a Le Mans race. But just in from puttering around on the street? I don't think so.

You can kill the engine at a red light because the turbo already cooled down (if it was hot in the first place) while you were slowing to the light.

If you are hypermiling, then your turbo probably didn't get too hot to begin with.

If you're constantly flooring it trying to gut the engine, then your turbo will be glowing red, but then you probably don't care about saving fuel anyhow.

Turbos on diesels don't glow red anymore. 15 years ago when NOx output was barely regulated, they did. 1200F EGT, no problem. Modern de-NOxed diesels with high EGR flow (30-50% of the intake charge) can barely make 800F EGT.

That being said, I wouldn't recommend shutting it down at red lights. Modern diesels need to keep heat in their aftertreatment systems. It's not like a gas engine that will merely pollute more if the cat cools down too much. A diesel will get constipated pretty quick if proper aftertreatment temps are not maintained.

Yea I'm not gonna risk it.

The new common-rail VWs will run more regen cycles to keep the DPF burned out, and end up wasting more fuel.

Keep it running.

But when the engine is idling the exhaust gas' temperature is too low to burn out soot/PM, so it does not help the DPF. On the other hand, it may produce more PMs for the DPF to catch.

Low load (idle) -> low EGT -> more PM, less NOx
High load -> high EGT -> less PM, more NOx

Just about all European low CO2-emission (<100 g/km) cars now have stop-start systems.
Just about all of them are diesels.
They have improved starter-engines, though diesels already had beefier starter engines.

Don't kill it when it's still cold though.
Once it's warm, forget about yer old sayings, old habits.

Like I said... if you're driving gently, it's probably not such a big deal... but VGTs are very sensitive... much more so than regular turbos. If there's an auxiliary pump that keeps the coolant and oil circulating even with the engine off, no problem. I've driven a lot of new turbocharged cars where there's a ridiculous amount of whine and thrum coming from under the hood even after the ignition is turned off, so I suppose they already do something like this for many cars with VGTs.

I imagine you've probably made slow progress gettintg to the button you need to get out and press, so Turbo is probably cool enough. But as far a turbo cooling goes, whether it is coolant or oil cooled if it is hot, ie just had a real hard run and stopped, the engine does need to idle for a few minutes to cool the unit down and allow the turbine bearing to stay lubricated while turbine slows down.
A lot of new vehicles may well have shutdown protocols, but that does not necesarilly mean it is appropriate for all vehicles.
Is it really 1 minute to get out and press a button and get in and drive on?
My vote is less than 1 minute leave it running.
1-3m, whatever you think is appropriate.
More than 3min, shut it down.

When city driving, I never hit the boost, engine temps are struggling to get up, luckily I don't need to drive in city that often, even rare is that I would meet traffic lights.

I turn off engine at traffic lights, but mostly when I know stop is tad longer, cool off is happening all the time at city driving, that is if you are driving sensible, as one is idling most of the time when hypermiling at city, so there is no difference for me when turning it off normally or at traffic lights.

It is not really fuel saving, but noise saving, why to keep making lot of noise when one can sit in silence?

Don't know about modern things, but I'm not too fond of them either, I can make old one to go as little or even less fuel because less of weight :)

That is about as close as one can get. A long traffic light, so what?, whereas waiting for a train would be different.

Some of these diesels are hard to turn over. And a pair of $200 batteries doesn't make that any easier with multiple stop/start. One could too easily find the limit on the wrong day in the wrong place as to how many re-starts without full re-charge on the batts. Or wear down a $400 starter too soon. Etc. It's a different budget for maintenance & repairs versus book guidelines.

I always feel so sorry for the local diesel owners; evidently they have to go through hell and high water to get their engines started and so once running, they never shut them off.

What? All they have to do is turn a key? Who knew! :eek:

Tell us more about the Diesel stop-start systems. Which manufacturers us them and in what models? Its very interesting.

Before we argue.

Do you think about how much diesel parts cost?

$180 reman Starter for F350. THANK GOD for lifetime warranty.

It get 3-5 sec for oil pressure come on so I rather leave idle. It only use .30-.60 GPH at idle. Turn off and turn on it will go up 1.20 gph for about 20 seconds then start go lower.

Agreed, I'd like to know this as well.
My input is that it's not worth shutting down for such a short period of time. But, then my experience is with an older diesel, and I certainly wouldn't do that to an old Turbo-diesel.

There is -- at least according to one recent press release -- a stop/start system planned for at least one line of trucks by one manufacturer in the works. I'd admit that a factory system would have my attention. But I'd not be willing to be first by any means.

+1
It is easy for others to spend your money on turbos, starters and batteries.

There's a variety of diesel technology out there and it's important to distinguish between the different technoologies. First off, let's cover the turbo issues. Historically, turbos were fixed geometry/wastgated and used only oil to cool them. The issue with a hot shutdown there is that when the engine stops so does the oil flow, so the oil near the hot metal of the turbo can coke up. This is because of all the heat that's stil in the metal of the turbo and the fact that oil won't thermal siphon very well. Many modern diesels (but not all) have variable geometry turbos with electronics attached. The electronics require much more cooling, thus engine coolant is used for cooling in addition to oil. The coolant won't coke up like the oil will, and will also thermal siphon so that the oil doesn't coke. So hot shutdowns with oil-cooled turbos are a no-no, whereas it's fine for one with coolant cooling.

Now, as far as aftertreatment goes, this varies greatly with the specifc engine. Whether you have EGR, SCR, DPF, NOx adsorbor, etc. The tuning is also very different for different applications. In some cases almost all the DPF regenerations are done "passively", i.e. no extra fuel required. In other cases "active" regenerations are required. Some applications also have special "warm up" modes that they'l go into to keep the SCR warm, and/or do a DPF regen. It's impossible to make a blanket statement the "Modern diesels all work this way..."

• Audi A2 "3L" with 1.2 TDI
• VW Lupo "3L" with 1.2 TDI
• Citroën Nemo with 1.3 HDi
• Peugeot 308 and 508 with 1.6 e-HDi
• Renault Scenic with 1.5/1.6 dCi
• Kia Cee'd with 1.6 CRDi
• Škoda Octavia, Superb and Yeti "GreenLine" with 1.6 TDI
• BMW 118d
• Mercedes-Benz E200 CDI

There are enough Start/Stop-equipped cars in Europe that the special batteries for those systems are now easy to find.

Just about all manufacturers.
Stop-start has gone mainstream.

Adding to the list of manufacturers :
Volvo, Mini, VW, ... well, just about all of 'm.
Not just on small diesels BTW - you could get a 3.0L BMW diesel with start stop system.

I'd be surprised if it caused lubing issues in a modern diesel engine.
Surfaces will already have been oiled by then, so there'll still be a film of oil on them. Can't compare a restart with a cold start.

It's not mainstream at all among American or Japanese manufacturers :/
I have a ton of respect for BMW (really German manufacturers in general) as they really pack a ton of sophisticated stuff into their drivetrains, I hope this makes the Japanese consider upping the level of tech in their engines!

I agree with what has been said earlier about EGT's being lower. Coking really only occurs in a turbo that has just been run really hard above 1,000 degrees and shut off with no cool down time at all. if your driving like a granny your turbo probably won't ever spool up so you won't have any worries about heat soak.

Pretty much so, also new watercooled ones are so much better in this aspect and modern synthetic oils that starting stopping is much more possible than it used to be.

However especially with longer engines like 6 cylinder ones, there is head warping/cracking issues with sudden temperature changes, so that is another thing to keep on eye when starting/stopping diesel.

I think that efficient P&G will not be very possible with such motor, where you get lot of heat variation, also longer head don't like to be pushed hard when not evenly warmed up, but starting stopping at traffic lights is probably not an issue at all.

Love your engine, care and listen it and it will give plenty of economical mileage :)

Hi,

I am still new at this, but here's my 2c worth...

I have an old diesel turbo, no electronics, no EGR, oil cooled turbo, mechanical Bosch diesel pump etc.
I found that it is not worth switching the engine of at most traffic lights, with the cycles varying from 20 sec to 30 sec. Thus not even a minute.

What I do however do is glide down hills with the engine switched off. HOWEVER, I keep the vehicle in 5th gear with the clutch pedal pressed down, and the ignition switched ON. Starting the engine, while still moving, is a simple matter of releasing the clutch.
If that truck of mine (2 metric tons) is hurtling downhill at 80mph with the engine off, the brakes do very little in terms of stopping the vehicle.
I any emergency situation, I need the engine back on in a split second. No time to fiddle with keys to start, just pop the clutch and it's back on.
Gentle release of the clutch starts the engine quite easily without any jerk, and there is no stress on the starter motor.
Driving like an old woman (or worse) means the turbo is not spinning at 18000 rpm when I cut the engine either.

I plan to install a Volt meter to monitor battery condition, in addition to an alternator cut-out switch. That way I will not be caught off guard without power in the battery.

If you have vacuum assisted brakes, those should provide three full stops with engine off, that is at least law in here and all cars generally seem to work so. It might be that there is problem with vacuum assist servo if you have poor brakes without engine running, which might be worth to check.

I tested the "theory", and got no assistance from the servo, at 400 000km and 14 years of service, the system may need some attention.

Another "pro" of re-starting without the keys is that you do not activate the glow-plugs every time.

My car doesn't have a turbo - I do notice that when stopped and idling at the lights my Ultraguage shows a rapidly dropping short average FC sp, if I have to stop more than a few seconds I do tend to switch off.

This would be nice, with my car however, I would need kill switch to get this behavior as shutting engine with keys turns it off, turn key to on position and glow plugs do their cycle, starting itself does not make glow plugs run, turning power to on setting will do that.

With diesel, kill switch should be rather simple to install however, there is shutdown solenoid somewhere and kill power to that and engine shuts off.

That old diesel engine of mine has one single electrical wire going to the Bosch diesel pump. If you cut power to that, the diesel is cut off.

If you supply power to it, and turn the engine, it runs. Simple. Also makes the immobilizer easy to override!

similar to my P7100, I'm sure. A big solenoid to pull a fuel cutoff lever.

With my old iron, I will shut down every time I'm out of the rig. Not going to shut down at lights, but do put it in neutral to reduce engine load and fuel consumption. Sitting in the middle of a busy intersection is not the time to find out you need new contactors. There is absolutely no safe braking with the engine off, so besides being hard on the trans I cannot coast.
No warm up time here, either. Once the transmission and brakes have pressure I'm moving, albeit slowly. It warms up just fine on a slow roll out to the faster roads.

Hardly anyone buys American vehicles over here - and the Chevrolets they sell here, aren't really American anymore - but the Koreans and Japanese have gone along with stop/start on their newer models.

It results in about 8% less fuel burn on the NEDC, and ever more countries are introducing a NEDC based taxing system, so not having a start/stop system can start costing customers as it make a vehicle less attractive.