240 General: Fuel consumption

[loki_the_glt]

With the older, manual box examples, and especially those with carbs, coasting (i.e. engine at idle, gearlever in neutral) will gain you some mileage improvement as the throttle is closed. You'll still have servo and PAS, but will lose some time when you have to react to a situation. Modern engine management systems automatically close off the fuel supply when the throttle is closed, but mech fuel systems keep puring the stuff into the combustion chambers so all you can do is minimise the amount you're using.

Auto boxes can't betreated in this fashion as the torque converter will die under these conditions, for the same reason that you can't bump- or tow-start an autobox

[Clifford Pope]

Originally Posted by loki_the_glt

Modern engine management systems automatically close off the fuel supply when the throttle is closed, but mech fuel systems keep puring the stuff into the combustion chambers so all you can do is minimise the amount you're using.

Yes, a fuel injection system will shut off the fuel when the throttle is closed, as on over-run, but it has to feed fuel in to keep the engine idling, exactly the same as a carburettor does.
So there is certainly no advantage in coasting in neutral with an injection system - it will use more fuel than just lifting off the pedal on a downhill section.

With a traditional carburettor it uses very little fuel at idling, but lots on overrun if there is no mechanism for shutting off the fuel. Later carbs do cut off the fuel on overrun, so again, the advantage lies in easing off the pedal rather than coasting in neutral.

I suspect any advantages (which I doubt) from coasting in neutral will be thrown away anyway by the need to speed up the engine once drive is required again. If you simply connect an idling engine to a gearchain doing perhaps 50 mph you will put strain on the clutch and gearbox.

I think the greatest single fuel saver is anticipation of traffic ahead and of road conditions and incline, so as to minimise the need for both accelerator or brakes. Brakes are the greatest fuel waster. Think of the brake pedal as a tap for ditching fuel over the side as from an aeroplane - you have used all that expensive fuel to gain momentum, and then throw it all away again by touching the brake pedal.

[Aminorjourney]

Yes! anticipation is key to energy saving

If you have, like me, owned and driven an electric car where every move results in wasted energy (and reduced range) you learn when to accelerate, when to not bother, and when to plan to stop. I guess it's just transferred over to the Volvo

Nikki.