engine off and coast question

[PaleMelanesian]

Oh I understand DFCO very well. It uses zero fuel. But it's not always the best approach to making mpg. It also eats up a lot of momentum. I burned fuel to make that momentum. I want it to take me as far as it can. DFCO adds an unacceptable amount of drag.

Yes, I'm in and out of N and D all the time. Back and forth and back and forth. At least on a Honda automatic (my personal experience), that's the way to get the best mileage.

Yes, while slowing for a turn or a stop, DFCO is useful as you're slowing AND not using gas. But you could start neutral coasting sooner and you don't have excess speed to burn off. You spent unnecessary fuel to be in that position, so DFCO is only a least-bad solution. Better to not need any braking at all.

[davelobi]

Pale, please don't be offended, I didn't mean that to sound like it did I guess.
Your longevity on the site and impressive mileage numbers show that you know what you are doing. I wanted to elaborate on dfco for others who don't know about it. It isn't as obvious as other methods.
neutral coasting vs eoc vs dfco vs driving habits = why they made apples and oranges. Something for everyone.

[PaleMelanesian]

What's great about some cars is the transmission is programmed to go into a pseudo-neutral coast just by lifting off the gas pedal. A lot of GM models do this that I know of. On the other hand, Honda's programming puts it into pretty harsh engine braking and DFCO every time you lift off the gas. I'm fighting that programming whenever I drive it, so DFCO is kind of my enemy.

[serialk11r]

Another thing that works on Honda A/Ts in my experience is if the transmission has decided to use a higher gear than necessary for whatever reason and doesn't shift down, going to neutral and then back will make it select a higher gear.

[PaleMelanesian]

Oh yes. That's a great trick. Mine won't use 5th gear until 45 mph, but will then hold it down to 38 once it's in 5th. A quick D-N-D shift at 40 mph and it drops right in.

[figit090]

What about the brake booster when the engine is off?

Also, does an engine with a manual transmission use any fuel if coasting down a hill with 0 throttle, being pulled by gravity above idle RPM?

[davelobi]

Originally Posted by figit090

What about the brake booster when the engine is off?

Also, does an engine with a manual transmission use any fuel if coasting down a hill with 0 throttle, being pulled by gravity above idle RPM?

Brake booster will not be supplied with vacuum used to assist with your power brakes when the engine is off. You will have one or two pushes of the brake pedal with vacuum assist from what was in the booster and that is it. After that it will be very hard to push on your brakes but they will still work.

Your question about coasting down a hill (I assume you meant engine on and left in gear) with zero throttle is a method I use a lot. Go back a page and find my post (#18?) that has a link to DFCO. EOC will coast further but DFCO also uses zero fuel while in effect.

[figit090]

Originally Posted by davelobi

Brake booster will not be supplied with vacuum used to assist with your power brakes when the engine is off. You will have one or two pushes of the brake pedal with vacuum assist from what was in the booster and that is it. After that it will be very hard to push on your brakes but they will still work.

Your question about coasting down a hill (I assume you meant engine on and left in gear) with zero throttle is a method I use a lot. Go back a page and find my post (#18?) that has a link to DFCO. EOC will coast further but DFCO also uses zero fuel while in effect.

thank you!

[elhigh]

Originally Posted by figit090

What about the brake booster when the engine is off?

Also, does an engine with a manual transmission use any fuel if coasting down a hill with 0 throttle, being pulled by gravity above idle RPM?

If yours is a fuel injected engine, the computer might recognize the loading paradigm and provide no fuel while the engine is being driven by the tranny. Certainly a carbureted engine will continue to burn fuel, but only at a slightly above idle rate as the increased vacuum pulls a little extra fuel through the jet.

As for the brake booster, if you're still in gear but letting the car pull the engine, you're getting a strong vacuum into your reservoir the whole time (unless it's a diesel, YMMV). And even if you're coasting in neutral you should still have enough vacuum in your reservoir for a couple of stops.

If not, consider building or buying a supplemental reservoir to tuck into one of the unused spaces of your car, to provide backup.

[figit090]

Originally Posted by elhigh

If yours is a fuel injected engine, the computer might recognize the loading paradigm and provide no fuel while the engine is being driven by the tranny. Certainly a carbureted engine will continue to burn fuel, but only at a slightly above idle rate as the increased vacuum pulls a little extra fuel through the jet.

As for the brake booster, if you're still in gear but letting the car pull the engine, you're getting a strong vacuum into your reservoir the whole time (unless it's a diesel, YMMV). And even if you're coasting in neutral you should still have enough vacuum in your reservoir for a couple of stops.

If not, consider building or buying a supplemental reservoir to tuck into one of the unused spaces of your car, to provide backup.

thanks! excuse me if this is commonly searchable on here but since we're here... for those that shut of their engine and coast in neutral, then restart their engine, is there advanced wear on the engine upon restart due to low oil pressure, and do you use a starter or can you bump the engine with the clutch at speed?
How much mpg increase can you expect to gain? Sounds risky but worth it if you know what you're doing...