Does a car consume fuel under engine braking?

[Serp86]

OK - for example when going down a hill - which is more efficient? Letting the car in e.g. 3rd or pressing the clutch/selecting neutral?

 

[mugs]

From what I understand, no it does not. The momentum of the car keeps the engine running, so no fuel is needed.

On a modern car that is

 

[KLin]

As long as the engine is running, it's consuming fuel.

 

[Joemonkey]

The amount of gas going into the engine in both circumstances is the same isn't it? You aren't pushing on the gas pedal, so the engine is technically "at idle" I would think.

 

[Baked]

Does the pistons move when your car's moving?

 

[CombatChuk]

Originally posted by: Serp86
OK - for example when going down a hill - which is more efficient? Letting the car in e.g. 3rd or pressing the clutch/selecting neutral?

The throttle is closed when the engine braking is going on, it does use a little fuel but the same amount as it idling. So not much.

 

[Serp86]

Its a 2005 suzuki reno.

I know that shifting into neutral a small amount of petrol is used up so that the engine keeps revving.
But does the petrol injection cut off when the engine is turning 'forcibly' or not?

 

[Vic]

Does a car consume fuel under engine braking?

With modern cars, no. However, modern cars also use very little fuel while idling.

You should never coast in neutral. I'm not going to get into the ridiculous "OMG it's illegal!" garbage, I'm just going to say that it's a stupid and improper way to drive.

This subject has been beat to death on the internet many times in the past.

 

[Demon-Xanth]

On a fuel injected engine it can shut down the fuel flow. On a carburated engine, it cannot.

 

[dethman]

it consumes less.

 

[letdown427]

As was said, modern cars (fuel injected ones) do not use any fuel when coasting in gear.

 

[Don Vito Corleone]

Originally posted by: Demon-Xanth
On a fuel injected engine it can shut down the fuel flow. On a carburated engine, it cannot.

QFT. This is why it's actually more fuel-efficient to leave a fuel-injected car in gear while descending, as opposed to putting it in neutral.

 

[Serp86]

Originally posted by: Vic

Does a car consume fuel under engine braking?

With modern cars, no. However, modern cars also use very little fuel while idling.

You should never coast in neutral. I'm not going to get into the ridiculous "OMG it's illegal!" garbage, I'm just going to say that it's a stupid and improper way to drive.

This subject has been beat to death on the internet many times in the past.

I live in malta - a very small island with lots of twisty roads and hilly terrain, hence the thread

I never heard of such a law here , however i would think reaction time under neutral coasting would be slightly faster, if you keep the foot on the brake like i do. Under an emergency all you have to do is just push one pedal (brake) as opposed to lifting foot off gas and pushing brake + clutch (not pushing clutch will kill engine + brakes + power steering). Now if you keep the foo of the brake, it can turn into a situation where you push the wrong pedal, but that can also happen when in gear - so whats the point?

Then again my car has never exceeded 90mph due to lack of straight roads so there might be something i'm missing

 

[43st]

Originally posted by: Serp86
Its a 2005 suzuki reno.

I know that shifting into neutral a small amount of petrol is used up so that the engine keeps revving.
But does the petrol injection cut off when the engine is turning 'forcibly' or not?

You use gas if the engine is idling... you use zero gas if you're not pushing on the gas pedal and the car is in gear. If you're always pushing in the clutch and coasting to stop lights you'll notice a 3-5 MPG improvement by leaving the clutch in gear.

 

[DivideBYZero]

MAKE IT STOP! NOT AGAIN! :|

 

[JulesMaximus]

Originally posted by: DonVito

Originally posted by: Demon-Xanth
On a fuel injected engine it can shut down the fuel flow. On a carburated engine, it cannot.

QFT. This is why it's actually more fuel-efficient to leave a fuel-injected car in gear while descending, as opposed to putting it in neutral.

You should do that with all cars actually. But I do agree, a fuel injected engine will shut off the fuel injectors when engine braking.

 

[DivideBYZero]

Originally posted by: Baked
Does the pistons move when your car's moving?

Your brain stopped moving long ago.

 

[mattpegher]

Given a hill sufficent to shift into neutral for any apreciable time the engine will return to idle which is usually less than the RPMs of coasting in high gear. Not that this makes it worth it unless you find a really long hill

 

[Don Vito Corleone]

Originally posted by: Thera

You use gas if the engine is idling... you use zero gas if you're not pushing on the gas pedal and the car is in gear. If you're always pushing in the clutch and coasting to stop lights you'll notice a 3-5 MPG improvement by leaving the clutch in gear.

You're right in terms of the mechanics involved, but I don't believe anyone would enjoy anywhere near a 3-5 MPG improvement under any circumstances by doing what you describe. An idling car uses very little gas.

 

[Baked]

Originally posted by: DivideBYZero

Originally posted by: Baked
Does the pistons move when your car's moving?

Your brain stopped moving long ago.

 

[bigfil]

Originally posted by: KLin
As long as the engine is running, it's consuming fuel.

 

[mugs]

Originally posted by: Serp86

Originally posted by: Vic

Does a car consume fuel under engine braking?

With modern cars, no. However, modern cars also use very little fuel while idling.

You should never coast in neutral. I'm not going to get into the ridiculous "OMG it's illegal!" garbage, I'm just going to say that it's a stupid and improper way to drive.

This subject has been beat to death on the internet many times in the past.

I live in malta - a very small island with lots of twisty roads and hilly terrain, hence the thread

I never heard of such a law here , however i would think reaction time under neutral coasting would be slightly faster, if you keep the foot on the brake like i do. Under an emergency all you have to do is just push one pedal (brake) as opposed to lifting foot off gas and pushing brake + clutch (not pushing clutch will kill engine + brakes + power steering). Now if you keep the foo of the brake, it can turn into a situation where you push the wrong pedal, but that can also happen when in gear - so whats the point?

Then again my car has never exceeded 90mph due to lack of straight roads so there might be something i'm missing

I think the reasoning behind not ever coasting in neutral is that you could be in a situation where you have to accelerate quickly to avoid an accident. You'd have to really stretch to find a situation where that is true though. And even if you leave the car in gear, you'd have to be in the RIGHT gear or you'd be better off in neutral - so every time you come to a stop you'd have to downshift through every gear.

To me, the slim chance of being in a situation where I'm slowing down and suddenly have to speed up is not worth all that. Call me stupid if you will, I don't care.

 

[JulesMaximus]

Originally posted by: mattpegher
Given a hill sufficent to shift into neutral for any apreciable time the engine will return to idle which is usually less than the RPMs of coasting in high gear. Not that this makes it worth it unless you find a really long hill

Wrong. The engine is just spinning over in gear, the rpms don't matter because the engine is not pushing the drivetrain, the drivetrain is essentially driving the engine. There is little to no fuel going into the engine during engine braking.

 

[randay]

This is interesting. I am not sure of any of this myself, and I am not convinced yet for either arguement, anybody here that can explain this in detail?

 

[Vic]

Originally posted by: Serp86

Originally posted by: Vic

Does a car consume fuel under engine braking?

With modern cars, no. However, modern cars also use very little fuel while idling.

You should never coast in neutral. I'm not going to get into the ridiculous "OMG it's illegal!" garbage, I'm just going to say that it's a stupid and improper way to drive.

This subject has been beat to death on the internet many times in the past.

I live in malta - a very small island with lots of twisty roads and hilly terrain, hence the thread

I never heard of such a law here , however i would think reaction time under neutral coasting would be slightly faster, if you keep the foot on the brake like i do. Under an emergency all you have to do is just push one pedal (brake) as opposed to lifting foot off gas and pushing brake + clutch (not pushing clutch will kill engine + brakes + power steering). Now if you keep the foo of the brake, it can turn into a situation where you push the wrong pedal, but that can also happen when in gear - so whats the point?

Then again my car has never exceeded 90mph due to lack of straight roads so there might be something i'm missing

The reason you should always be in gear is because you should always be in complete control of the car. You are not in complete control while coasting in neutral. And have you not noticed that your car handles corners better while in gear as opposed to in neutral?