Freewheel Behaviour
Discussion
Was in a taxi today which does about 25 mpg, but the driver claimed that by freewheeling everywhere he gets about 35mpg.
Now I've known people to freewheel down long winding passes etc but this bloke was freewheeling down every hill.
Another thing that gets me is he kept saying his Engine Management Light keeps going off and on when driving.
He basically got to a hill and put the car in neutral and switched the engine off while still moving, then when he got to a level bit of road he switched the car back on while it was moving and put it in 2nd or 3rd and carried on.
Now i'm no expert but this seems like odd driving behaviour and would probably not be very good for the engine and/or gearbox and would the EML go on by doing this constantly.
basically i want to know is this normal?
would it screw up the car?
Now I've known people to freewheel down long winding passes etc but this bloke was freewheeling down every hill.
Another thing that gets me is he kept saying his Engine Management Light keeps going off and on when driving.
He basically got to a hill and put the car in neutral and switched the engine off while still moving, then when he got to a level bit of road he switched the car back on while it was moving and put it in 2nd or 3rd and carried on.
Now i'm no expert but this seems like odd driving behaviour and would probably not be very good for the engine and/or gearbox and would the EML go on by doing this constantly.
basically i want to know is this normal?
would it screw up the car?
Hypermilers do it. Nutters.
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
Edited by Disco You on Tuesday 13th May 22:41
No car these days injects fuel on the overrun - it's too easy a win for fuel economy. Chances are that he's wasting any gain by the moments just after starting when the mixture is enriched.
Also, driving a big car like a minicab usually is with no power steering (straight away) or servo assistance on the brakes (after a couple of brake applications) is dumb, especially when it's loaded up and going downhill.
Also, driving a big car like a minicab usually is with no power steering (straight away) or servo assistance on the brakes (after a couple of brake applications) is dumb, especially when it's loaded up and going downhill.
davepoth said:
No car these days injects fuel on the overrun - it's too easy a win for fuel economy. Chances are that he's wasting any gain by the moments just after starting when the mixture is enriched.
Also, driving a big car like a minicab usually is with no power steering (straight away) or servo assistance on the brakes (after a couple of brake applications) is dumb, especially when it's loaded up and going downhill.
Mostly true but...Also, driving a big car like a minicab usually is with no power steering (straight away) or servo assistance on the brakes (after a couple of brake applications) is dumb, especially when it's loaded up and going downhill.
The engine braking will reduce momentum at least on a manual if he stays in gear going downhill whether fuel is being injected or not, more if not, and hence energy (derived from fuel, ergo, fuel) is being wasted.
If he pops out of gear and freewheels then the engine is idling and definitely injecting some fuel.
So if you are into that sort of thing, there will be some effect.
I'm into something like this only when the gauge is close to zero and I have no idea where the next services are!
My Lupo 3L (an uber eco 100mpg thing) has a freewheeling function, it effectively dips the clutch when you lift off in any gear & reapplies the clutch if you touch the brakes or throttle. It genuinely adds to the mpg's but does require some driver forethought. Its amazing how far you can go especially in traffic or with hills. The lupo has no power steering though some had electro mechanical like many new cars do now. It was 10 years ahead of whats just around the corner now.
Bosch have just developed a hydro electric clutch actuator system for manual cars that does this and will switch the engine off. First car with it is a Peugeot I think.
VW Passat 170 DSG also has a similar function, 60mph coasting is using fuel at the rate of 450mpg-500mpg on tickover
The faster you coast the better the MPG's 
Bosch have just developed a hydro electric clutch actuator system for manual cars that does this and will switch the engine off. First car with it is a Peugeot I think.
VW Passat 170 DSG also has a similar function, 60mph coasting is using fuel at the rate of 450mpg-500mpg on tickover
The faster you coast the better the MPG's Edited by cptsideways on Wednesday 14th May 12:02
cptsideways said:
Expect your production car to do this shortly all by itself
And to have done it a long time ago! Rover P4 had this feature for efficiency, and Saab 96 had it to avoid wearing out the 2-stroke engine due to lack of lubrication on the overrun. I'm sure there are loads more, but I know of those two.Actually turning the engine off rather than just leaving it idling in neutral is probably a really bad plan though... No vacuum means brake servo will stop working after a small amount of braking, and no power steering isn't great either. Not to mention that you can't restart most cars without turning the key full off and on again which, will stop lights etc working whilst off. So what he was doing sounds mad.
If vacuum pump, power steering, etc, were all fully electric, then I don't see why a modern car couldn't automatically stop the engine whilst freewheeling. But, as far as I'm aware, modern cars which do freewheel (eg some VW group DSGs) currently leave the engine running at idle speed.
If vacuum pump, power steering, etc, were all fully electric, then I don't see why a modern car couldn't automatically stop the engine whilst freewheeling. But, as far as I'm aware, modern cars which do freewheel (eg some VW group DSGs) currently leave the engine running at idle speed.
Well, I've got a new game on the way home in which I try and coast from the top of a road all the way through a village.
https://goo.gl/maps/pfkg4
I have to accelerate up to about 45mph, then knock the E36 into neutral and coast to the end.
I think I enjoy it way too much.
https://goo.gl/maps/pfkg4
I have to accelerate up to about 45mph, then knock the E36 into neutral and coast to the end.
I think I enjoy it way too much.
New 911 has a 'coasting' feature on the PDK box..
http://flatsixes.com/cars/porsche-991/pdk-coasting...
I have a car from '65 that I can turn the motor off a good few minutes before arriving home cos it is all downhill, and no worries about servos and power steering, very satisfying..
http://flatsixes.com/cars/porsche-991/pdk-coasting...
I have a car from '65 that I can turn the motor off a good few minutes before arriving home cos it is all downhill, and no worries about servos and power steering, very satisfying..
I guess it depends on the engine, really old carb fuel and mechanical injection systems that use fuel according to airflow and nothing else would probably use less by sitting at idle whist the car coasts - anything made in the last 20 years that has mapped fuel management probably uses more just to keep the thing from stalling than it would using momentum to keep the engine spinning.
AJB said:
Actually turning the engine off rather than just leaving it idling in neutral is probably a really bad plan though... No vacuum means brake servo will stop working after a small amount of braking, and no power steering isn't great either. Not to mention that you can't restart most cars without turning the key full off and on again which, will stop lights etc working whilst off. So what he was doing sounds mad.
If vacuum pump, power steering, etc, were all fully electric, then I don't see why a modern car couldn't automatically stop the engine whilst freewheeling. But, as far as I'm aware, modern cars which do freewheel (eg some VW group DSGs) currently leave the engine running at idle speed.
This. Sounds incredibly dangerous. I think I would of asked him to pull over so I could get out.If vacuum pump, power steering, etc, were all fully electric, then I don't see why a modern car couldn't automatically stop the engine whilst freewheeling. But, as far as I'm aware, modern cars which do freewheel (eg some VW group DSGs) currently leave the engine running at idle speed.
996TT02 said:
davepoth said:
No car these days injects fuel on the overrun - it's too easy a win for fuel economy. Chances are that he's wasting any gain by the moments just after starting when the mixture is enriched.
Also, driving a big car like a minicab usually is with no power steering (straight away) or servo assistance on the brakes (after a couple of brake applications) is dumb, especially when it's loaded up and going downhill.
Mostly true but...Also, driving a big car like a minicab usually is with no power steering (straight away) or servo assistance on the brakes (after a couple of brake applications) is dumb, especially when it's loaded up and going downhill.
The engine braking will reduce momentum at least on a manual if he stays in gear going downhill whether fuel is being injected or not, more if not, and hence energy (derived from fuel, ergo, fuel) is being wasted.
If he pops out of gear and freewheels then the engine is idling and definitely injecting some fuel.
So if you are into that sort of thing, there will be some effect.
I'm into something like this only when the gauge is close to zero and I have no idea where the next services are!
I'd be willing to bet money that the taxi driver was riding the brake all the way down the hills to keep the speed in check, which completely defeats the point.
DanielJames said:
Well, I've got a new game on the way home in which I try and coast from the top of a road all the way through a village.
https://goo.gl/maps/pfkg4
I have to accelerate up to about 45mph, then knock the E36 into neutral and coast to the end.
I think I enjoy it way too much.
My cars a bit loud so my game started when I was getting home late one night.https://goo.gl/maps/pfkg4
I have to accelerate up to about 45mph, then knock the E36 into neutral and coast to the end.
I think I enjoy it way too much.
How far away from your house can you coast with the engine off to your parking spot. I can do 2 streets away, as soon as I make the corner into the road I can turn my engine off and using a couple of tiny downhill bits I just roll into my spot without braking to stop. Quarter of the time I have to push it the last meter once I've got out, which really pisses me off
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