[QUOTE]Originally posted by TrueDrezzer

 

Thinking about it..

If there is ZERO fuel going into the engine (or at least not enough to cause combustion), having the engine turn over from the wheels isn't a bad thing at all...

(Assuming no combustion is taking place), its simply moving air through the engine..big deal right? After all, its still lubricated, and not causing additional heat (no fire, no heat).

-- Aaron

 

^ it's not a big deal, but the air that is sucked into the engine is compressed every other time the piston goes to the top of the cylinder. that decellerates the car, and that loss of momentum will have to be regained later... thus using more fuel.

 

[QUOTE]Originally posted by Hockey

 

this is very true. some people argue that downshifting is bad b/c it wastes gas(higher rpm) BUT when i tell them that the engine uses no gas during engine braking, they change their minds.

 

you can test to see if the car uses gas during decel... just (CAREFULLY!) turn off the motor with the car in gear while you are coasting at like 4000rpm...

the car will sound like it's still on, in fact, you can just turn the key to on and it'll be back running, no starter

 

There was a time when I connected a vacuum gauge to my old car and noticed that I had good fuel mileage if I can keep the vacuum reading the highest. My IS300 also has a gauge that reads fuel mileage, and it does "go off the scale" during decel in gear.