December 30, 2010
which uses more fuel, coasting in neutral or no accellration in 5th gear?
Want to know if I can save more fuel by coasting down hill in neutral or if I save more by leaving the car in gear with zero acceleration. VW TDI
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Filed under Gas Conservation FAQ by on Dec 30th, 2010. Comment. 
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Comments on which uses more fuel, coasting in neutral or no accellration in 5th gear?
It’s a little tricky. Coasting in neutral uses the same amount of fuel as idling while parked. Coasting in gear, assuming the drivetrain is spinning the engine faster than idle speed, uses no fuel at all in a fuel-injected or diesel engine. The downside is that it slows you down a little so you may have to use more fuel to get back to speed.
I believe coasting in neutral is illegal. And you’re probably better off coasting in 5th as far as fuel consumption is concerned.
Coasting in neutral is dangerous. There are many fatalities that are related to this. Look it up.
5th gear
To amplify Eric P’s answer, while it’s true that a fuel-injected engine uses no fuel as long as you keep your foot of the gas pedal while the car is in gear (Doesn’t matter which gear), the engine is forced to turn at a higher speed than when it’s idling in neutral. This adds a bit to engine wear — It all adds up over time. The legality issue aside, I don’t think coasting in neutral is dangerous. What is dangerous is not keeping to a safe speed. That’s what brakes are for. On a long mountain descent I recommend staying in gear to prevent overheating of the brakes. By the way, many cars with automatic transmissions and old cars with overdrive have a freewheel function that result in coasting when you take your foot off the gas.
Yes it is against the law in most states to coast down hills in nuetral.
Neutral= Idle= Uses fuel
The rest of the guys haven’t a clue about engine management. The motor gets NO excessive wear during compression braking(coasting in 5th). It does use some fuel, not nearly what idle uses!
Use compression braking without worry! Do not coast in neutral. Enjoy life and quit worrying.
ASE Cert Auto Tech, 92 GTI16V 2.0L