Hypermiling a diesel

[slowmover]

Then again, I'm definitely getting nowhere near as good as Dave, and he's admitted to P&G techniques. His truck is also lighter, shorter, more aero and less rolling resistant than mine. And he has a better haircut . . . .

[TX_Dj]

Originally Posted by slowmover

And he has a better haircut . . . .

I'd believe that!

[euromodder]

Originally Posted by TX_Dj

I've always been a skeptic of P&G (even though I've seen evidence to say it works)

In a diesel it's not going to give as spectacular a result as in a gasser.
If - like me - you don't want to shut down the engine during the glide, the net result is likely going to be marginal.
I've tried P&G (engine on), and while it looked good on the ScanGauge, the tank average nor actually refueling showed anything out of the ordinary.
I've found it to be rather annoying to other drivers as well - one's hardly ever alon on the road over here.

I've resorted to pulsing pretty hard, then coasting (engine on) to transition points along my usual route - turns, curves, stops, lights, anything requiring a substantial drop in speed.
I've experimented with the speed and place combination that I need in order to arrive at the next transition point with a suitable speed.

On longer stretches of road, I still use a constant speed.

[UFO]

Originally Posted by euromodder

I've tried P&G (engine on), and while it looked good on the ScanGauge, the tank average nor actually refueling showed anything out of the ordinary.
I've found it to be rather annoying to other drivers as well - one's hardly ever alon on the road over here.

On longer stretches of road, I still use a constant speed.

I've reached the same conclusion with my VW diesel with automatic transmission. The Scangauge lies about P&G so I don't do it anymore; I just coast in neutral when I want to conserve momentum and DFCO when I have to slow or stop.

The Scangauge thing is really annoying actually. It is really lousy feedback when it comes to coasting and engine mods. I am keeping it only for the xgauges, the code scanner, and to test future aero mods.

[Vekke]

If you calibrate your scangauge to full P&G technigue it will show correct. I was not able to get correct figures to other/both techniques. So you can calibrate it to what technique you use the most.

[TX_Dj]

Great info. I'll play with it some more once I've got my ultragauge installed and calibrated correctly... maybe I'll see some effects in the end.

I know that on my most hilly trip, which I take a few times a year, I do see a difference if I DWL up the hills and coast neutral down the hills rather than maintaining a target speed... so I'm not saying that techniques like P&G are snake oil, I just have trouble seeing how they can be as effective as some folks say they are unless your transition points make use of terrain so you can convert potential energy into kinetic...

The UG should also help me determine (and monitor) the optimal throttle position for efficiency for those tests as well.

[UFO]

Originally Posted by Vekke

If you calibrate your scangauge to full P&G technigue it will show correct. I was not able to get correct figures to other/both techniques. So you can calibrate it to what technique you use the most.

I was doing some P&G where the SG reported very optimistic mileage, and when the tank was filled the mileage ended up worse than constant speeds and coasting. That's the main reason I don't do it, other than it annoys other drivers, and nobody needs to do that.

The traffic I drive varies from day to day, so over the course of two weeks between fill-ups my SG tank mileage will be off by +/-5% or more, so calibration from tank to tank is useless. My driving technique is as constant as it can be. If the silly SG could just figure out how much fuel is being consumed a bit more accurately, it would be a very useful tool. As is, not so much.

[slowmover]

The UG should also help me determine (and monitor) the optimal throttle position for efficiency for those tests as well.

Yup. "Real time" on a heavy pickup appears to make the gauge a necessity.

[tinduck]

Originally Posted by euromodder

In a diesel it's not going to give as spectacular a result as in a gasser.
If - like me - you don't want to shut down the engine during the glide, the net result is likely going to be marginal.
I've tried P&G (engine on), and while it looked good on the ScanGauge, the tank average nor actually refueling showed anything out of the ordinary.
I've found it to be rather annoying to other drivers as well - one's hardly ever alon on the road over here.
(...)
On longer stretches of road, I still use a constant speed.

Nearly the same over here. I use p&g only on slightly downhill parts of the road to extend coasting in neutral (engine on). On a flat road, it seems to be useless with my combination of TDI and large CdA. On steeper declines, I DFCO to stay inside the speed limit.
ScanGauge wise, this seems to work but I have yet to see a record tank while driving with SG. Unfortunately, the cold season is ahead, so a comparison between good summer/autumn tank mileages and using SG over the winter is rather unfair, I guess the real effect (if any) can be seen next spring when conditions get better again.
Furthermore, the gas stations seem to have switched to winter diesel now, especially my uphill fuel usage has risen by at least a litre/100km according to SG, and flat road fuel usage is up a bit too.

so long,

tinduck

[Vekke]

In finland there is so little traffic that its not a problem most of the time. I can confirm if there is even one car behind me its not so fun to do it specially if the car behind be dont keep safe distance. Some will notice what I am doing and keep enough distance so it does no harm to them. Some will drive in the bumber and usually in that case I start to slow down so much that person will pass me. usually 10 km/h speed under the limit is enough. So I courage people to pass me in those cases.

Bigger truck are not the same case as small hatchbacks that is sure but on downhills you should see some gains with P&G. Next week I will be in a 60 tonn truck trailer combination to teaching hypermiling techniques so I will learn also myself more about the situation with big trucks.