[Mike K]

In trying to stretch my $$$ fuel dollars a wee bit, I’ve taken to coasting up to that red light a ways up ahead lately. My GM auto trans keeps rpms typically higher as it downshifts through the gears when coming to a stoplight.

But if I shift to neutral, my e91 just loves to coast. It actually picks up speed while the rpms stay low at idle. Am I saving fuel? Or, am I being “fuelish”?

Any harm in this O’ wise ones?

[Brian86]

Don't do it.

Your car turns off the fuel injectors when coasting. It is burning fuel idling in neutral.

Any difference one way or the other is completely trivial.

[Tambohamilton]

I'd coast in-gear too, but apparently an established economy tactic is to accelerate and coast out of gear repeatedly instead of holding a steady cruise. Seems odd to me really, but there it is.

One thing for sure is that the longer you coast either in gear or in neutral, the better it will be for your economy Vs driving then braking (hard).

[ryanful]

Originally Posted by Tambohamilton

I'd coast in-gear too, but apparently an established economy tactic is to accelerate and coast out of gear repeatedly instead of holding a steady cruise. Seems odd to me really, but there it is.

One thing for sure is that the longer you coast either in gear or in neutral, the better it will be for your economy Vs driving then braking (hard).

This worked in carbureted vehicles. As mentioned above, with fuel injection, most systems completely shut off the fuel flow with the accelerator is lifted and the vehicle is coasting IN GEAR, until an idle condition is needed.

[Tambohamilton]

Just playing devils advocate...

Could the extra drag of the engine turning above idle speed offset the gains of zero fuel use, Vs longer coast with the engine using bare minimum fuel?

Personally I feel that my car drinks fuel disproportionately when I accelerate Vs a steady cruise, and I doubt coasting either way would offset it. Though coasting as much as possible to slow or stop is of course worth it. I'd normally coast in gear anyhow - don't want to use my brakes!

[owdi]

Coasting in neutral burns more fuel than staying in gear. When in gear, the momentum of the car can be used to drive your accessories. When coating, have to burn fuel to spin the engine.

https://www.popularmechanics.com/car...-fuel-economy/

[Tambohamilton]

Originally Posted by owdi

Coasting in neutral burns more fuel than staying in gear. When in gear, the momentum of the car can be used to drive your accessories. When coating, have to burn fuel to spin the engine.

https://www.popularmechanics.com/car...-fuel-economy/

That article is specifically about coasting downhill, where of course coasting in neutral will use more fuel because you'll be using your brakes to compensate. Coasting to a stop, on the flat, is different because coasting in neutral will let you coast for longer and possibly offset the small amount of fuel used to spin the engine at idle.

Clearly the correct answer is to coast in neutral with the engine off

[Want_1]

Kill the engine and coast in neutral only way to do it.

[marvinstockman]

Do a controlled highway test, coasting and not coasting, and report your findings.

[Mike K]

Hey all, thanks for all the thought provoking input! Knowing the injectors shut either way means using engine braking not only drives the alternator but yields the same economy as neutral coasting and saves brake wear too.

[C4maro]

Does driving in limp mode improve fuel economy on n54?