Quote:
Originally Posted by TP 135i
Except that you must be using SOME fuel or the engine would stop running. It's not like the engine is OFF while you are coasting down hill.
I've wondered which uses less fuel....coasting down hill in gear or coasting down hill out of gear. Logically if you are out of gear in a down hill coast you are using the same amount of fuel as you would be while idling at a light. Are you using the same, more or less if you are coasting down hill while still in gear?  |
Actually no, as others have stated, the injectors do not fire at all. There is NO fuel being used. Modern engines like ours simply let the pistons go through the 4 strokes - using the spinning of the wheels to do so. When you put your foot down again, the injectors will fire.
If you're out of gear, then the engine must use fuel to maintain idle speed. So in essence, it should be more efficient to coast down in a high gear.
Which means the most fuel efficient way to coast down a hill is to select a gear which keeps engine speed just above idle (so the injectors won't fire) as this minimises speed loss through engine braking.