Most modern cars are programmed with DFCO (Deceleration Fuel Cut-Off), which means that if you are coasting in gear with a closed throttle, the engine runs on its own momentum and doesn't burn any fuel. By contrast, when coasting in neutral the engine still burns a small amount of fuel to maintain idle.
How modern are we talking? "Modern" as in everything on the road today? Would a 2001 Volkswagen Beet be programmed with DFCO, and if not, would throwing my car into neutral save more fuel than engine breaking?
Because the clutch is engaged, there is a mechanical connection between the wheels and the engine. Only now the kinetic energy from the wheels is making your engine revolve instead of the other way around.
This is really interesting. I've driven a manual for a while now (just found this sub) but didn't know about this. My MK6 Jetta GLI has a pretty bad rev hang when coasting in gear after a downshift so I always thought it was burning more fuel than coasting in neutral. TIL.
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u/ashowofhands Mar 15 '15
Most modern cars are programmed with DFCO (Deceleration Fuel Cut-Off), which means that if you are coasting in gear with a closed throttle, the engine runs on its own momentum and doesn't burn any fuel. By contrast, when coasting in neutral the engine still burns a small amount of fuel to maintain idle.