Car coasting fuel saving

[Daimo]

Something I remember from a few years back.

Driving along, come to a downhill section.

You take it OUT of gear, and the engine still needs ignition and fuel to keep it turning over as the clutch is not engaged and needs the fuel to keep it turning over.

But.

If you leave it in gear, the wheels are still spinning the engine, there-fore no fuel needs to be injected to keep the engine running, so effectivly you're getting free mileage.

Is this actually true? I've been coasting when-ever appropriate, and whilst its not going to save me a whole load of juice, I reckon i'll save a good 10+ miles just by coasting down particular roads on my way home.

Obviously you can argue that you use this fuel going up the hill, but my routes to and from work are slightly different so I would be going up less steep inclimbs going up, than I do coming back home.

But does that actual theory work, or is the engine still pushing fuel in (off throttle in gear coasting) hence making my outlook total BS?

Or does this only work on more modern engines (2002 powerhouse Fiesta 1.25 whoooop whoooop).

[Wafer_Thin_Ham]

Yes it is true. Works on all relatively modern engines. Depends on your exact engine/ECU though.

Used to work on my 2000 petrol 2ltr Focus. Put it in fifth and then you have minimum engine braking too.
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[P.]

Its still injecting fuel regardless...once the engine is turned over its injecting.
If you say... switched it off, left in 5th gear and made sure you was on a hill and your steering lock wouldn't come back on... ... you could coast the hill and bump by lifting the clutch at the bottom and continue on your way.


I havent tried this in any car at all...honest...

EDIT : saw big_hams post.. really? didnt know that would work

[Daimo]

I wont turn it off, thats dangerous, esp in a commuter traffic.

So it is still injecting fuel, but is it actually burning?

[Kickstart]

Hi

If the throttle is closed and the revs reasonable it probably cuts the injectors. So going down hill with the throttle closed you are probably using no fuel at all.

If you dip the clutch then the revs will drop to idle and the injection system needs to supply fuel to stop the engine stalling. Hence you will be using fuel.

This isn't a particularly new thing. My 20 year old Alfa 33 is set up like this (noticeably above idle rpm with less than 5 degrees of throttle from memory). However it won't apply to most things with carbs.

All the best

Keith
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[bikertomm]

I'm always in 5th letting it pull itself along... or down long downhill sections I just neutral it, thought it has to be more saving than just leaving it in gear and letting the revs build up!


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[lihp]

[Kickstart]

[Daimo]

Yeah thats what I thought. The wheels turning means the engine is rotating hence keeping it running.

Im just kinda questioning if it actually still fires fuel in whilst doing it though.

Fezzy Zetec 1.25 isn't carb'd, its FI, so presumably its not putting fuel in.

[lihp]

[fatpies]

[Daimo]

Ace, free miles

Gotta make factory figures somehow. Still, a 1.25 engine only making 40mpg is still lame But then financially, how can you justify spening £6k+ on a car that'll give you 60mpg. It'll take years to recover the losses, with the only added bonus of having a newer car.

Festers only got 41k, for £1500, so atm, I dont think I can justify it.

I spec'd up a new Vauxhall Corsa LE last night (alloys, sideskirts etc). 1.3 cdti, £16.6k before i'd done anything else. Seriously, £16k for a corsa?

My first corsa was £11.5k for a brand new 1.6 16v Sport. WTF??????

[shereen]

When you coast you have less control of the vehicle - I would rather have my brakes at 100% stopping power than save a couple of quid on petrol. What if you squashed a kitten because you couldn't brake fast enough?

Is it really worth it to save on 10 miles of go go juice?
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[Kickstart]

[The Artist]

The amount of fuel used at idle is minimal though. The simplest thing to do would be to put in neutral at the top of hills and coast down. Yes it will use fuel but it will be such a small amount it is negligible compared to actually using the engine to pull the car along.

[fatpies]

[Kickstart]

[Andy_Pagin]

My Sierra used to switch itself off on hills all by itself, unfortunately it was always when going up a hill.
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[Daimo]

[Daimo]

[Kickstart]

[Daimo]

[fatpies]

[The Artist]

[Daimo]