"Dave Plowman (News)" wrote in message
...
Either you increase the engine speed as you change down thus wasting
petrol or you let the clutch speed up the engine wearing it more than
needed. And not all cars cut off the fuelling totally on the over-run.

For cars that don't cut off the fuel totally on overrun (I thought all cars
with fuel injection did cut off) is the amount of fuel used dependent on
overrun revs? In other words, will they use more fuel in a lower gear
(changing down to give engine braking) than a higher gear (staying in top
until you're ready to set off). And is it more or less efficient to brake in
gear or to press the clutch?

My car uses *some* fuel (instantaneous mpg shows as about 250) if I press
the clutch and let the engine idle, but uses *no* fuel (mpg
shows as 999) if I stay in gear and let the car slow down on overrrun.

I wonder how much fuel is used in accelerating the engine to match a lower
gear before going down a long hill? Is it a measureable amount?