How do you eco-drive a diesel ?

[instarx]

Originally Posted by MazdaMatt

physics aside... I also am looking for ways to more efficiently drive my big (huge) diesel truck. It is less aerodynamic than a brick and weighs between 5000 and 8000 pounds depending on the load.

23L/100km...what is what, about 6 gals per 63 miles? 10-11 mpg?

I have an 8,000 lbs diesel van and I know how you feel. I get 16-17 highway, but could get more if I didn't use 100% biodiesel. I think there are a few things you can do easily:

1. Inertia management: This means never using your brakes, not fully stopping at stops signs, and taking the best line in any corner. Keep as much velocity as you can at all times so you don't have to regain it with the throttle. It's funny that your truck won't coast well. My heavy van coasts forever. Throw it in neutral. On the highway I accelerate gently to over the limit going downhill and then use minimum throttle going up the next hill, letting the van gradually slow down to under the speed limit.

2. Use highway tires and not agrressive tread tires. My mileage dropped by 4 mpg when I went from highway treads to M&S. Grrr.

3. Don't accelerate too slowly. Get up to speed fairly quickly and then back off the throttle. Try to get in high gear as soon as you can. Having said that, 2,900 rpm shift points seem WAY high for a diesel.

4. Although this doesn't improve mileage, it does save gas - use a GPS to plot your routes. Plot both the shortest route and if you have multiple stops let it plot the most efficient order of the stops. GPS is the most underused gas-saving tool on the planet IMO. If you save just one mile out of ten that's a ten perent improvement.

5. Change your oil to a lower viscosity one. I use 0-40W in my diesel year round and I do notice a difference engine friction and starting.

6. Make sure your radiator fan clutch isn't frozen. That will cause huge mileage losses.


You may have transmission gear ratios set up for city driving and not for highway use. That would make sense with the Hostess truck and would explain those high rpms. Chaging the final drive ratio is not that hard to do and could help a lot.

[MazdaMatt]

Thanks for your input!

Yes, this truck coasts like it has square wheels. It is because (guessing by the feel) the torque converter likes to lock up. My previous CAR was an automatic (its been a while), but i recall that when you let off the gas, the revs would drop to idle and it would coast forever. This truck will actually engine brake all the way down to about 20km/h.

Definatley it is set up with city driving in mind! This thing handles like a minivan driving through downtown areas... even with my race car in the back and all my gear.

My tires are all M&S tires that I bought from a junkyard... I expect that they are pretty hard due to age, so that helps a little, but still, they are all-seasons.

Re: gps... i don't drive this thi ng all over th eplace, only to race tracks or when moving stuff. I ALWAYS plan out not just the shortest route, but the route that will best allow me to cruise at 70km/h over flat terrain... i'm quite anal about saving gas in this thing!

I will read up on the oil possibilities... i will need a change after it has been parked all winter.

I asked google and it says that 23L/100km = 10.2mpg. Bleh.

oi... frustrating. Glad I don't have to drive this thing daily!

[instarx]

Originally Posted by MazdaMatt

This truck will actually engine brake all the way down to about 20km/h.

Hostesss may have done that on purpose to save brake wear. That may have been a good idea when fuel was $1/gallon, but not so hot these days.

Look into having someone change your top gear for a highway gear. If you get the engine RPMs down 25% that's a 25% improvement in fuel economy (I think). You may be able to tell what your drive gear is by a plate on your transmission, or on the options list sticker if it's still there. Or it's possible to calculate the gear ratio by knowing speed (true speed, not speedometer speed), engine RPM and tire diameter.

[MazdaMatt]

according to my gps, my speedo is dead accurate from bottom to top

Having a mechanic replace a gear is totally out of the budget of this truck. That stuff is NOT cheap to do. Even replacing the final drive is not a cheap thing to do since i can't do it myself. I was also thinking about the final drive thing... if i did that, then this gutless p.o.s would spend more time in second gear because any moderate hill requires that i floor it to keep my speed up.

I think my best option is to just sell the damn brick and buy a big V6 manual truck and an aluminum trailer... I just don't like the idea of daily driving a V6 truck. (i would have to sell my car as well to afford a decent one)... although, if i could find a deisel manual then i could consider a veg conversion down the road.

[TestDrive]

From MazdaMatt's posts - sliced, diced and transmographied

1994 Ford F350 box truck
7.3L Diesel
3-speed auto (C6)
Axle ratio - unknown
Tires & rims - unknown
----------------------------------------------
It began life as a Hostess (cupcake) city delivery truck.
Currently use to transport a track car.
Less aerodynamic than a brick.
Weighs ~5000 lbs empty & ~8000 lbs loaded.

Normal acceleration upshift is around 3k rpm.
Throttled deceleration downshift is around 2k rpm.

It is REALLY frustrating to be at 62km/h (38mph) @ 2900 rpm and the damn thing isn't shifting.

Redline is about 3200rpm.


It seems my THREE-SPEED tranny shift 95% based on speed and just barely based on load.
ie, accelerating up to 65, i can drop throttle and it will upshift,
or i could not drop throttle and it will shift at 70.
If i DO drop throttle, by the time i'm in the new gear, i'm only doing 61-62 and any amount of throttle will cause it to downshift again

Constant throttle is no good.
If I'm doing 80km/h (50mph) on the flat and reach a SLIGHT up-slope,
it will slow to about 65km/h (40mph) and down-shift.
Then that throttle position can't maintain the high revs and i slow down even more.

I drive 85-90 (percent of the time?) on the highway at 100km/h (62mph)
I drive 70km/h (43mph) in the 80km/h (50mph) zones.
My last trip was ~23L/100km (~10 mpg)

A city delivery truck designed to live in 2nd gear - not surprising you're unhappy with it's performance on the highway.

Originally Posted by MazdaMatt

Hostess apparently had a rock-solid maintenance schedule and the second owner runs a small trucking company. I can ONLY ASSUME that the fluids are doing fine, but who knows if that tranny is correct or the valve body is correct... he may have scooped it up chneap from an off-road racing buddy. I woudl LOVE it if i could replace a 40 dollar part and have it start upshifting at 2000rpm instead of downshifting at that!

Ok, let's assume Hostess had a rock-solid maintenance program. Ford's on-line maintenance schedules only go back to 1996, but let's assume '94 F-350 and '96 F-350 have the same schedule. According to Ford transmission fluid is to be changed every 30,000 miles and no mention of the filter. (You'd be hard pressed to find a transmission mechanic who wouldn't suggest changing the filter at the same time - but no knowing what Hostess decided was best). Did Hostess sell/trade the thing at 85,000 miles - 5,000 miles before the third transmission service. No chance the guy before you decide right away that he wasn't keeping it for long (too doggy on the highway) and decide to skip the 90,000 service - let the next guy do it?

The cheapest thing that MIGHT help would be a $20 vacuum modulator. You can test the integrity of the diaphragm by attaching a short piece of vacuum hose and sucking on it like a soda straw. If it won't hold vacuum, it's shot. A bad one will usually cause harsh shifts (clunk) and may move the upshift point to slightly higher rpm. You probably don't even have to drop the filter pan to replace it if it's bad. If the vacuum line leading from the engine to the vacuum modulator looks at all funky or cracked, replace it first.

The next cheapest thing that might make a difference is a $40 transmission filter. Add $$ for xx quarts of transmission fluid and 30-60 minutes labor charge if you don't do it yourself. Only special tool required is a large, wide drain pan and not at all difficult to DIY.

A dirty transmission filter can cause delayed shift and or shift hesitation.

Originally Posted by MazdaMatt

Funny enough, i think the best mileage trip i ever had, i spent about 3 hours in first gear at idle... it was stop/go traffic and i played the accordian by simply sitting there iwthout touching the pedals.

Originally Posted by MazdaMatt

But moving backwards a little... what about driving technique? I follow trucks and i drive f'ing slow, i try to maintain speed at the lowest possible in the highest gear... i refuse to neutral coast because i did that once and it clunked HARD on every shift for the next hour of driving.

Try the back-roads and keep to 2000-2200 rpm as much as possible. Higher rpms only when accelerating to get to next higher gear. If you can't keep to 2200 rpms or less, drop back a gear. Slow and steady wins the FE race.

[MazdaMatt]

Wow, thanks a bunch for that. One correction though (my bad)... i meant that i drive 85-90km/h on the 100km/h highways. Coincidentally, i also drive about 85-90% of the miles on the highway as you stated. With a shift point of ~65 and comfortable cruise of 70 (that is, comfortable because i'm a little above the downshift point so i don't need to worry about +-2km/h), then my highways cruise of 85km/h is not very high into third gear.

Again, thanks for putting it all together.

[TestDrive]

Originally Posted by MazdaMatt

Again, thanks for putting it all together.

You're welcome.

Based on parts look-up, Ford just slapped in the exact same 3-speed C6 as they use with gasoline engines - no adjustment for diesel's much lower power band.

I'd still try to find a good, (probably not Ford Service Center) transmission mechanic (does nothing but work on transmissions, transfer cases and differentials) to discuss this with. At worst you'll waste some time tracking one down and talking to him. At best, he'll tell you that you need a $90 Transmission Shift Kit, $40 Transmission filter, xx(12?) qts fluid @ $3 per quart and 2 hours @ labor rate and life will be dramatically better. I'm not saying that's the case, but it is entirely possible that it's the case. Putting in a shift kit isn't the same thing as rebuilding a transmission. I know it's not very labor intensive on some transmissions, but have no idea about C6. I'm also completely not sure that it would address your problem, but I notice that only diesel engines are listed as compatible with the above kit!

Again, good luck. Have a great day.

[ConnClark]

Originally Posted by instarx

WARNING! Fluid dynamics post!



I just woke up and will address many of your points later (you made some good ones, but mny are still incorrect) - but first, that picture.

That, that...thing , does not measure what you think it does. Note that the pressure appears to be LOWER in the area with high velocity air. But this is exactly the opposite of what you claim should happen when velocity pressure adds to static pressure, so how can that be? It is because the apparatus actually demonstrates the Bernoulli effect, where high-velocity air moving across an opening creates a localized low pressure area proportional to its velocity.

I never claimed velocity added to static pressure. I claimed that variing velocities in the intake piping would effect the measured pressure drop across the intercooler depending upon the points the pressure readings were taken.

If you read up on bernoulli's equation air moving across an opening has nothing to do with it. It is directly related to the velocity of the air and nothing to do with an opening.

This is also a mechanism that produces lift on an airfoil. The air moving faster over the top of the airfoil causes a drop in static pressure in reference to the slower moving air below the airfoil.

Those manometers are not measuring the static pressure along the tube, but the relative strengths of the three localized low pressure areas created by the Bernoulli effect. It is not possible to even estimate the static pressures along the tube with that poorly designed apparatus (who would ever connect three manometers in series like that - you can't tell which is measuring what). That contraption is a perfect example of how somone who doesn't understand the principles (not you, the people who put it together) can design an "experiment" or demonstration that they only think illustrates their point (unless the caption to that picture is "Demonstration of Bernoulli Efect" or "World's Worst Design of a Pressure Measuring Apparatus Using Manometers").

Actually that is a commercial science kit sold to and used by universities. Yes it is used to demonstrate Bernoulli's principle. It also demonstrate that just like in plumbing of an intake system with an intercooler static pressure rises and drops according to the velocity of the fluid at different points in it, hence the difference in the fluid levels.

A general comment about your interpretations of the relationships between velocity and pressure: Be careful not to confuse cause and effect. Air movement (velocity) is caused by pressure differentials, but the inverse is not true - air pressure is not changed by a parcel of air simply being in motion. This is true in air systems ranging from continental-sized weather systems, to air being pulled through a duct, to the air moving around in your living room.

If what you say is true would you care to explain why the pressure increases again after flowing through the constriction.

As the experiment in the picture demonstrates the static pressure in the wide part of the pipe before the constriction is the highest because it has the lowest water level. As the pipe narrows the velocity increases and static pressure drops thus raising the water level in reference to the water level before the constriction. As the narrow pipe widens again the velocity drops and static pressure rises again. This is proven by the water level drop in reference to the water level at the constriction.

[MazdaMatt]

That shifter kit...

i suspect that it is diesel only because (i think) bully dog is a diesel performance parts company. Does "increased transmission pressure" mean lower shift points, and does it mean higher risk of blown seals and leaks?

I have a pretty good understanding of cars and engines, but auto trannies and diesels are my weakest points.

In the spring (when i next need my truck) i will call up a TRUCK tranny shop and see what a fluid change, shift kit and oil change will cost me. Might make all the difference that I need...

[TestDrive]

> i suspect that it is diesel only because (i think) bully dog is a diesel performance parts company.

Could be, I'm not familiar with Bully Dog

> Does "increased transmission pressure" mean lower shift points, and does it mean higher risk of blown seals and leaks?

Honestly, your guess is as good as mine. Did I mention you need to talk to a transmission mechanic?

> I have a pretty good understanding of cars and engines, but auto trannies and diesels are my weakest points.

Doubt I'm more than a few paragraphs further along in the trannie & diesel service manual than you are.

In the spring (when i next need my truck) i will call up a TRUCK tranny shop and see what a fluid change, shift kit and oil change will cost me. Might make all the difference that I need...

I'd start by describing symptoms and you problems with symptoms and see what they suggest. If they say: shift kit + filter + fluid + not too much for labor = lots better, then go for it.