Quote:
Originally Posted by Isaac Zachary
I still don't get it. I'd want fuel to be cut to the engine any time my foot is off the pedal, whether I'm coasting in neutral or engine braking. I don't see an advantage of keeping the engine idling at any speed. Why?
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Safety: It you cut fuel and turn of the engine anytime you lift of the throttle you go to full engine braking. This is braking separate from the hydraulic braking system and the ABS system can't control it. In low traction situations engine braking alone can be enough to lock the wheels and cause the vehicle to lose control. (RWD truck, unloaded, downhill, on snow)
This is one of the reasons that you don't find high speed automatic emergency braking on manual transmission cars.
You also wouldn't want to car to lurch forward if someone hit the throttle with the car at a stop, in gear, with the clutch engaged. A manual car should only start when in neutral or when the clutch is disengaged.
Convenience. Shifting into neutral to turn off the engine gives the driver control of when it happens. There can be plenty of cases where the driver might not want the engine to turn off. A 95 degree day in humid Alabama stop and go traffic comes to mind from personal experience. (I didn't buy a Civic Hybrid because it didn't have an electric AC compressor and the AC turned off at stops)
Longevity: For long life you want your engine to come up to operating temperature quickly. Turn your engine off every time you lift the throttle could cause the engine never to come to operating temperature. (This is why hybrids don't turn off the engine until it comes up to temperature)