Is there any point to P&G in a diesel?

[bluetwo]

Originally Posted by rmay635703

Pulse and gliding a NATURALLY APIRATED diesel is almost pointless.

My 1982 diesel Suburban I drove for years with a 3speed auto and 4.10 gears got the best MPGs accellerating very very slowly and holding constant speed and coasting to stop. I could get around 22mpg in town and approx 21.2 on the highway if I was careful.

I do recommend letting the vehicle slow uphill and speed up going down however, thats all I did to get decent mileage from such a poorly configured rig. heck I was in 3rd at 15mph or so.



The way you are stating things...

??? Its sounds as though you are more jaded than concerned. You are using loaded statements like killing a child because of slow driving or non-constant speed driving. When I am doing something on the road other people aren't doing, like obeying the posted speed limit or slowing to yield at crosswalks or even pulling off to the right to yield to other drivers in a hurry. I pay VERY CLOSE ATTENTION TO WHAT I AM DOING!

Unlike 90% of the drivers on the road, if driving is what I am doing that is all I am doing and I am focused on it. Hypermiling requires you to pay close attention to everything around you and everyone around you to anticipate your next action, if everyone drove as hypermilers do people would have their attention on the car and the road around them and not on the other BS they usually do.

I have a feeling many here have excellent driving records even with "unsafe" practices as you deem them.

I doubt anyone here will be in a massive accident because of hypermiling, likely obeying the law might get them in an accident but for the wrong reason.

I hope you can understand why we might object to your language choices.

And for the record, there are more deaths of children in and around parking lots/driveways than on the open road. I somehow doubt slow driving would increase that number.

You're just taking what I'm saying the wrong way and you need to chill. I haven't said anything wrong and I'm trying to help a common good.

[rmay635703]

Originally Posted by bluetwo

You're just taking what I'm saying the wrong way and you need to chill. I haven't said anything wrong and I'm trying to help a common good.

Many terrible things are done with good intentions for the common good, just as I took your words the wrong way your statements could spark the wrong someone to make another bogus law that could lead to unnecessary harassment of normally law abiding individuals. We need to keep as many of our remaining freedoms as possible.

We don't need any association implied between hypermiling and law breaking / unsafe driving. An important part of hypermiling is predicting your coarse of travel so you can most effectively obey the law from point A to B

The Law won't differentiate between us and them once a myth gets propagated into law.

And "Those people" is you and me.

Also as I mentioned elsewhere, many of us have vehicles that behave the same way running or not, my Subaru has mechanical brakes and steering that operate without the motor running, my old suburban was steerable and the brakes worked without power as well (just harder to push the brake pedal)

I won't further clutter this otherwise excellent thread anymore and my posts can be deleted if the mod prefers.

Cheers
Ryan

[roflwaffle]

Originally Posted by Frank Lee

I'm thinking no.

I'm thinking the biggest reason P&G works is simply due to the percentage of time the engine is off.

Perty much.

The only engines I can think of offhand that have really nice BSFC ovals are newer heavy duty ones (I think thi is from a DT 466), and even those can see a ~25% increase in FE through judicious "load leveling", so to speak. Older diesels, as well as most gassers, can still see a significant (greater than 25%) increase in efficiency by trading consistent low load operation for periodic high load operation, given the same vehicle energy requirements of course. Obviously, if the operating conditions permit it, and it's available, taller gearing can do the same thing w/o the hassle, but that isn't always an option.

[roflwaffle]

Originally Posted by rmay635703

Pulse and gliding a NATURALLY APIRATED diesel is almost pointless.

My 1982 diesel Suburban I drove for years with a 3speed auto and 4.10 gears got the best MPGs accellerating very very slowly and holding constant speed and coasting to stop. I could get around 22mpg in town and approx 21.2 on the highway if I was careful.

That's because you have very short gearing coupled to an automatic transmission. Unless there's a lock up clutch, you're SOL because higher torque levels tend to result in in greater losses, up to ~35-40%, w/ automatic transmissions, and w/ a turbo 400 and 4.10 gears, you can't even drop down once you get going fast enough. P&G in the Camryaro is only worthwhile if the TCC is engaged IME, which requires a significant downslope and hopefully a wind at my back. Under those conditions I can bump up against 40mpg, and that's including a quarter of my drive time spent idling. W/ a manual trans I could probably get mid-40s over the same route by cutting off the engine and minimizing high load trans losses.

[roflwaffle]

Originally Posted by MetroMPG

Do modern diesel passenger vehicles not have vacuum reserves for one or two full-assist stops with the engine off, like every gasoline car I've ever driven?

My diesel merc has a booster, and it's almost a half century old. AFAIK, diesels came w/ boosters the same time gassers did. It's not like vacuum pumps were anything new when we started seeing more boosters.

[cfg83]

JacobAziza -

When I was on a business trip in Brussels in 2007 I got to drive this :

2004 Renault Megane Sedan with 1.9 liter dCi engine



One nice thing (assuming the ScanGauge was reading correctly), was that when I pulled my foot off the accelerator pedal in gear, the Scangauge showed 9999 MPG, meaning DFCO (deceleration fuel cutoff) mode was present.

What I am implying is, with a modern diesel drivetrain, P&G should give you infinite MPG during the (in gear) coast.

CarloSW2

[Christ]

Originally Posted by cfg83

JacobAziza -

When I was on a business trip in Brussels in 2007 I got to drive this :

2004 Renault Megane Sedan with 1.9 liter dCi engine



One nice thing (assuming the ScanGauge was reading correctly), was that when I pulled my foot off the accelerator pedal in gear, the Scangauge showed 9999 MPG, meaning DFCO (deceleration fuel cutoff) mode was present.

What I am implying is, with a modern diesel drivetrain, P&G should give you infinite MPG during the (in gear) coast.

CarloSW2

I may be wrong about this, but I believe that several older diesels with chain or gear driven pumps that didn't use ECU's also have DFCO, in the ability of the pump to stop pumping when the (throttle) lever is pulled back to the min-stop, then the speed governor will actuate the throttle at lower speeds to pick up the fuel input and make it idle.

I'd love for someone to step in and correct this, as it may be a complete misconception, and I've never tested it.

[Christ]

Oh, and that car looks like it was pure sex to drive. I think I like it.

[cfg83]

Christ -

Originally Posted by Christ

Oh, and that car looks like it was pure sex to drive. I think I like it.

Yeah, I really liked the proportions of the Megane sedan :



It just looked "right" to me.

When I looked at the car (without knowing the price), I wanted it. But I think if it were sold in the USA it would suffer from the "VW Effect", i.e. parts too expensive and too hard to get.

This Megane was a company car, so it had been abused. It had a terrible "clunk" when I turned the steering wheel all the way. But I'm not complaining. I won't complain about getting to drive a 6-speed diesel on the company's tab.

CarloSW2

[roflwaffle]

Christ, some gear driven diesels did have DFCO more or less, although it depends on the pump governor. VE pumps w/ variable-speed governors can do this, but not ones w/ a min-max-speed governor IIRC. That said, most pumps, at least in small cars from the 80s on, have a 12V solenoid/plunger to cut fuel that's only active when the ignition is set to run so even if the pump has a min-max-speed governor someone can setup a separate cut-off for this and have DFCO on demand.