[cefncoedjess]

Can anyone clear something up for me, i have been told by various people that if you freewheel down a hill with the engine ticking over you will use some fuel, however if you go down a hill in fifth but with you foot off the pedal you will use NO fuel!!! is this true and does it work with my CDT 2.0 Rover 75?
Please advise

 

[*Mike*]

Surely, if the engine is turning over then its using fuel???

 

[cefncoedjess]

Yes i understand that but as it has been explained to me and been on Top Gear that modern cars if you take your foot off the pedal whilst going down hill you will use no fuel at all?? i cant see it somehow but you never know

 

[ashy]

I agree with Mike, no matter what, the engine is using fuel if it's running. If it didn't the car would simply cut out. The only thing that reduces the amount of fuel is reducing the revs. You can dive the car out of a plane in neutral you still won't save any more fuel if you don't keep the revs low.

 

[cefncoedjess]

So am i better off frewheeling in neutral or leaving it in 5th gear with foot off pedal?

 

[ashy]

So am i better off frewheeling in neutral or leaving it in 5th gear with foot off pedal?

Neither, you use the appropiate gear to control the car. Coasting is illegal as far as I know.

 

[RevorTD]

IMHO which is as an amateur. If you coast downhill with the engine on then the engine will be at tickover using fuel. Whereas with - now I'm guessing - your foot off the throttle and in gear at a rpm higher than tickover you would need no fuel going through. I know thats how it works on some Trucks anyhow. :minxy:

 

[mikehIOW]

as freewheeling is illegal, or atleast not recomended, I'd go with the 5th option (however I freewheel all the time when I'm low on petrol )

for the record, freewheeling uses the same petrol as idle (duh!) I read in my old calibra manual that 3 minutes of idling is the equivalent of 0.6 miles of grandad driving.

Just for the record, that was for a 2.0 car though.

 

[RevorTD]

IMHO which is as an amateur. If you coast downhill with the engine on then the engine will be at tickover using fuel. Whereas with - now I'm guessing - your foot off the throttle and in gear at a rpm higher than tickover you would need no fuel going through. I know thats how it works on some Trucks anyhow. :minxy:

This should be the case with diesel EDC types.

 

[cefncoedjess]

so it is true i will use no fuel going downhill in 5th gear well.. well

 

[mikehIOW]

you'll use some fuel, not no fuel at all, but very little yes.

 

[E_T_V]

Not sure on the BMW engine but on the L series if you are driving at above 1200rpm without applying any throttle then all fuel is cut from the engine.

 

[ashy]

Well in neutral the car would simply just idle so some fuel would be used otherwise the car will cut out. The ECU will maintain the revs.

In gear the revs will be controlled by the rate the gear box turns the crank until the ECU detects a situation where it thinks the revs are too low and the car is in danger of stalling for instance as you decelerate. At that point the car can't be made to go any lower than normal idle. The ECU will see to that. The point can be proved by simply taking your foot off the accelerator in gear. The car will not stall as the ECU will control the throttle.

 

[Homer]

From what I know most engines have a switch which when the car is moving by whats left of its momentum, the engine is being driven by the car in effect and fuel is cut off.

I know for a fact that my mums Corsa has this, and I wouldn't be at all suprised if something such as a Rover 75 had it aswell.

 

[NIGEL25]

Most modern cars do cut fuel on over run to cut emissions and save fuel also improves engine braking fueling will start again just before tickover.

 

[evolotion]

not sure on diesels, but as said above petrol cars tend to have an over-run fuel cut (my mems 1.6k certainly does, my wideband o2 says so )

in that when the engine is going downhill and throttle is closed there is NO fuel injected into the engine. if you coasted down the hill you would definately use fuel as the engine is idleing. there is no rperequisite to use 5th gear either, any ger can be used. only stipulation is that the throttle is closed.

 

[cefncoedjess]

Thanks that clears things up a bit, i just wish that i knew it definately worked with the 75 cdt

 

[crofts]

Fuel Saving

Only thought that comes to mind is :- what speed will you be doing at the bottom of the hill and how much fuel will you use to resume speed or, worse, to climb up the next hill ? I think there's no chance of perpetual motion to enjoy here. Think I would be bored stiff and probably nodd off when speed dropped to 10 MPH or less.............. if it's a long hill of course ! ! !

 

[BENZS180]

Don't suppose you have any tips for saving petrol on motorways

Only i suffer a condition called lead foot and people have trouble keeping with me

Oddly not the police though!!!!!!!!!!:sad3:

 

[Mike T]

Fuel saving

A block of wood under the go pedal would help to save fuel. Don't do this on the stop pedal though!
(Previous advice to be taken in the spirit it was given!!!)