Which drive technique uses the most fuel.

[edwardmk]

I've always coasted down long hills when safe to do so, but I noticed that when I coast down a hill in my 2005 Astra I get 130mpg on the instant consumption, but 999mpg if left in fifth gear on engine braking. Presumably the ECU is cutting off fuel under certain conditions to reduce fuel consumption? Do any of the 75/ZT models do this?

[macafee2]

Never coast, the driving wheels should be engaged with the engine, safety!
I engine brake. I think you are right, the ecu cuts off fuel but does it only cut it down to the amount used at tick over?

macafee2

[guru]

Yep never coast, always leave it in gear as the ECU will shut off the fuel supply whereas when coasting it's still using fuel to keep the engine spinning.

[Torqueofthedevil]

Originally Posted by guru

Yep never coast, always leave it in gear as the ECU will shut off the fuel supply whereas when coasting it's still using fuel to keep the engine spinning.

But the engine is still sipping fuel when left in gear! Otherwise it would stop! Nothing wrong with coasting, makes perfect sense in some situations and I'm not at all convinced that the supposed safety concerns have any validity.

[SD1too]

Originally Posted by Torqueofthedevil

Nothing wrong with coasting ...

Hello Charlie,

Coasting, that is making progress with the engine disconnected from the driving wheels, is actually dangerous. Braking distances are increased markedly together with the tendency for the car to understeer to an alarming degree.

What is the point of it?

Simon

[Torqueofthedevil]

Originally Posted by SD1too

Hello Charlie,

Coasting, that is making progress with the engine disconnected from the driving wheels, is actually dangerous. Braking distances are increased markedly together with the tendency for the car to understeer to an alarming degree.

What is the point of it?

Simon

I would suggest simply to slow down gradually, making best use of the car's momentum while using minimal fuel, in a situation where best brake performance and cornering ability aren't needed.

[COLVERT]

Originally Posted by SD1too

Hello Charlie,

Coasting, that is making progress with the engine disconnected from the driving wheels, is actually dangerous. Braking distances are increased markedly together with the tendency for the car to understeer to an alarming degree.

What is the point of it?

Simon

I coast everywhere.----Locally half my journeys are in neutral.---

67 years plus on the road with never an accident or even a near miss.

Could be that I enjoy driving and get pleasure at every moment at the wheel and not just something to get from A to B.--I constantly judge my performance and position on the road and that of other road users.

I owned two Austin Westminsters over a period of 14 years.--The gearbox had a freewheel attachment fitted which meant the car never had engine braking.
Taking my foot off the throttle meant the engine went straight into tick over.

The clutch was never needed to change gear you just put the gear lever wherever you wanted.--Brilliant idea but never used in modern times.

That started me into free wheeling every where.----

[macafee2]

Originally Posted by Torqueofthedevil

But the engine is still sipping fuel when left in gear! Otherwise it would stop! Nothing wrong with coasting, makes perfect sense in some situations and I'm not at all convinced that the supposed safety concerns have any validity.

I dont think the engine with fuel injection consumes more fuel then at tick over. It does not draw fuel, fuel is forced into the engine by throttle position and a closed throttle will not send fuel above the tick over amount to the engine.

If you dont think coasting is a safety concern, go somewhere quiet and see what cornering speeds you can achieve coasting and driving around the corner. Worse, is part way round the corner is to coast. You need to be going at speed so you need a big un off area. Try it.

macafee2

[Torqueofthedevil]

Originally Posted by macafee2

I dont think the engine with fuel injection consumes more fuel then at tick over. It does not draw fuel, fuel is forced into the engine by throttle position and a closed throttle will not send fuel above the tick over amount to the engine.

If you dont think coasting is a safety concern, go somewhere quiet and see what cornering speeds you can achieve coasting and driving around the corner. Worse, is part way round the corner is to coast. You need to be going at speed so you need a big un off area. Try it.

macafee2

I'm not going to try it, because cornering isn't a situation where I would let a car coast! Likewise, if I'm coasting and something happens and I need to brake, I can put the car back into gear in less than a second. But as per my previous post, in some situations (eg no corners, empty road - half a mile from a roundabout on a quiet dual carriageway might be one example) I don't see any harm in it at all.

[MSS]

Originally Posted by edwardmk

I've always coasted down long hills when safe to do so, but I noticed that when I coast down a hill in my 2005 Astra I get 130mpg on the instant consumption, but 999mpg if left in fifth gear on engine braking. Presumably the ECU is cutting off fuel under certain conditions to reduce fuel consumption? Do any of the 75/ZT models do this?

When coasting the engine is basically idling and using fuel. On the overrrun the fuel is reduced to the absolute minimum as it is the wheels turning the engine.