driving downhill - fuel consumption

Do you save fuel by taking the car out of gear going downhill or would that actually use more fuel?

Reply to
grape
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grape gurgled happily, sounding much like they were saying:

Depends on the car. Anything with vaguely modern engine management will cut the fuel on the over-run, but obviously not on idle, so you will actively be using more fuel by coasting.

However, besides the amount of fuel saved being utterly miniscule, you're also not in proper control of the car. Don't do it.

Reply to
Adrian

Possibly a few pence worth, but it is illegal and potentially dangerous.

Reply to
Mrcheerful

Not in proper control? Owzat then? I coast, I've always coasted and I always will coast when it's safe and appropriate to do so.

Ian

Reply to
Ian

Is it illegal? My jeep had a "coast" button on the steering wheel that , well, made it coast funnily enough when running on cruise control. Also, at speeds less than around 45mph, when you lifted off the throttle, the revs dropped to tickover and it coasted.

Mike P

Reply to
Mike P

Ian gurgled happily, sounding much like they were saying:

No, neither do I.

Reply to
Adrian

Same with cars like the Saab 96 that had freewheel devices, innit. I don't remember them all being illegal.

Reply to
Willy Eckerslyke

Highway code says no.

Reply to
grape

If it is illegal they could never catch you. How would they know?

Reply to
grape

Maybe there is a legal difference between a freewheel device and actually putting it in neutral? Some old Rovers certainly had a freewheel and that obviously was legal, and there seem to be many other instances coming to light in this thread, but they are all devices that allow the vehicle to roll on, BUT the car still remains in gear with no need to turn the device off to accelerate. Certainly it is easy to find references to coasting being illegal in many USA states, so the Jeep system is presumably ok there. The highway code says don't coast, but actually finding chapter and verse as to legality is not instant!

Reply to
Mrcheerful

By watching 2 tonnes of Jeep fly past almost silently?

Mike P

Reply to
Mike P

Experience also says no, unless it's just tootling at 30/40 on slight gradients - although I don't bother.

Coasting down hill on mountain roads at 50 is a definate no-no.

Reply to
Pete M

According to the display on my Picasso, I get anything up to 999.9 mpg when traveling downhill. How much more do you think I would get by coasting?

Reply to
pb

When they find you dead in the ditch with the car in neutral?

Reply to
Peter Hill

Couldnt get it into gear officer.

Reply to
grape

advanced 'Hypermiling' enthusiasts will do that and switch the engine off too, then bump start the car at the bottom of the hill. Save fuel but punish the drivetrain!

Reply to
Mark W

Citroen should use that in their advertising. I'd buy a car that did 999mpg even if it was French.

Reply to
Mark W

No need to take it out of gear, just declutch.

It depends on what you have to do at the bottom of the hill. If you let the car overrun you'll use no fuel on the hill, but you'll be going slower by the time you get to the bottom. Declutching will mean the car uses a small amount of fuel to idle on the hill, but you'll be going faster at the bottom.

If you can make use of the extra speed by leaving it later before accelerating again, then the coasting method will be more economical. If there is some need to brake at the bottom, wasting the extra speed that coasting gives you, then overrunning will be best.

Of course, the most economical way would be to declutch and turn off the engine, but the safety crusaders might point out some... erm... minor niggles that causes with the steering and brakes.

Cheers,

Colin.

Reply to
Colin Stamp

Tried that. Rolling down a long hill, followed a few twists in the road, then suddenly 'click' 'panic' 'screech'.

Luckily I'd made sure there was nobody else around before experimenting..

Also, is a bump start from the wheels any more punishing than using a starter motor? I wouldn't have thought so. Doesn't feel like it.

Reply to
PCPaul

I wouldn't have thought that using the starter motor impacted on the transmission at all...

Chris

Reply to
Chris Whelan

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