Originally posted by: Mark R
Originally posted by: DivideBYZero
Originally posted by: JulesMaximus
Coasting downhill is not going to save you any fuel whatsoever. When coasting in gear you are using zero gas anyway. Coasting in neutral you are actually using fuel to keep the engine at idle.
No. If I coast in gear the engine will turn and I will lose fuel.
Not in a modern car.
In a modern car, the ECU will sense the car's speed and recognise the fact that it is in gear - and that the car's rolling momentum will keep the engine turning. The fact that the car's momentum is enough to keep the engine going allows the ECU to shut off the fuel completely during engine breaking.
When the car slows down to just above idle, the ECU will turn the fuel back on.
If you switch to neutral, there's no momentum connected to the engine to keep it turning - this means the engine has to keep turning under its own power. This means it needs fuel, and the ECU will continue to deliever fuel to it.
You will use more fuel coasting in neutral than coasting in gear, for this reason.