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Originally Posted by reb01501
Just because you can coast in neutral with the engine running, does not mean you should. Modern engines cut off the fuel to the the cylinders when coasting (DFCO)
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Sure, but then you're braking (=wasting energy).
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so shifting to neutral would actually use more fuel than if you left it in gear, unless the engine braking is enough to force you to use throttle to maintain speed.
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In the end, you'll use less fuel - even though the engine is idling and using fuel to do so.
The difference is in the braking (DFCO / engine braking) - or not braking (coasting).
You'll coast far further than when letting go of the throttle and go into DFCO.
That's where the gain is.
(If not, the tranny has some kind of freewheel in it that automatically lets you coast.)
Coasting has become my main way of reducing speed - whereas I used to use DFCO all the time, it's now my second means of slowing down, with braking only coming third.
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Shutting off the engine while in neutral will indeed save gas, but is controversial due to safety considerations.
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You loose powersteering and (after a few dabs at the brakes) power brakes. That's my main reason not to shut off the engine.