Fuel consumption: putting car in neutral vs taking foot off the accelerator

[Just-ify]

I was wondering, on older carburetor cars I found an improvement in fuel economy if you put the car in neutral when going down a hill.

Now with the fuel injected e36 and its fuel consumption indicator I found the opposite - that taking your foot off the accelerator indicates better consumption than putting it in neutral.

Really confused... any ideas?

 

[Doomsdaya]

Free Wheelie :rollsmile:

On idle the gauge sits at the highest... OBC shows eco at 39.5 L/100km :hammerhead:

On a polo its the opposite... on idle the eco shows 1.1 L/100km :thinking:

 

[killua]

On a carburetor car the engine still gets fed fuel when in gear and slowing down. This is more than if you would have just left it to idle...
In fuel injected car, the engine is barely given fuel (probably only a little bit for lube) when car is in gear and slowing down...

So on carb: free in neutral, Injection: keep in gear.

 

[moranor@axis]

on injected cars the car will not fuel when the wheels are turning the engine... when you put in neutral there has to be fuel added to keep the engine turning...

 

[Spy007]

Buy Diesel

 

[Bayn46]

I only put my car in neutral at stop lights to preserve the clutch.

 

[Just-ify]

I only put my car in neutral at stop lights to preserve the clutch.

I never thought of that... on that note, one can flip the car out of gear into neutral easily without depressing the clutch or getting any grinding sound. Theoretically that would save you a clutch operation - can you think of any reason doing that would damage the car?

 

[Bayn46]

I only put my car in neutral at stop lights to preserve the clutch.

I never thought of that... on that note, one can flip the car out of gear into neutral easily without depressing the clutch or getting any grinding sound. Theoretically that would save you a clutch operation - can you think of any reason doing that would damage the car?

I assume you mean while moving otherwise you would be pretty screwed if you did that at a stop :rollsmile:

There is a technique called rev matching that allows you to change gears by maintain a certain RPM and you don't need to depress the clutch. Never tried it and don't plan on doing it but on that principle you should be fine pulling the car out of gear while moving (difficulty would depend on your current RPM). I don't really have the technical understanding to be 100% sure though

 

[Jandre]

I only put my car in neutral at stop lights to preserve the clutch.

I never thought of that... on that note, one can flip the car out of gear into neutral easily without depressing the clutch or getting any grinding sound. Theoretically that would save you a clutch operation - can you think of any reason doing that would damage the car?

I assume you mean while moving otherwise you would be pretty screwed if you did that at a stop :rollsmile:

There is a technique called rev matching that allows you to change gears by maintain a certain RPM and you don't need to depress the clutch. Never tried it and don't plan on doing it but on that principle you should be fine pulling the car out of gear while moving (difficulty would depend on your current RPM). I don't really have the technical understanding to be 100% sure though

I used to do this often on my brother's Ford Capri a few years ago.

He snapped the clutch cable a few times, and then I had to get the car home.

Pop her into second, and start her. It's a bit of a jerk to get going, but then you sit with your fingers on the gears, lightly pushing/ pulling it towards neutral. Once you match the revs it easily slips into neutral. By playing with the revs, it easily slips into 3rd, 4th etc.

Did it with an e30 325i too.

The trick is not to get caught up at a stopstreet or robot.

But if it happens, start from scratch again.

wouldn't recommend it if you don't need to though

 

[Spy007]

:biglol::biglol: I love A/T

 

[kabal]

how does putting it in neutral at a stop save the clutch compared to pushing in the pedal? when you push the clutch pedal, it is not engaged, therefore there is zero wear

 

[Bayn46]

how does putting it in neutral at a stop save the clutch compared to pushing in the pedal? when you push the clutch pedal, it is not engaged, therefore there is zero wear

Fully depressed is fine but a lot of people sit at 1/2 clutch when stopped which can't be healthy. Also depends on how springy your clutch is. I put it in neutral because I prefer to not have to keep the pedal to the floor.

 

[Raybimmer]

When going down hill the fuel injection will cut fuel supply at over 1500 revs or so then feed fuel as the revs drop below that , you may feel the power come in .
The clutch release bearing takes strain if you hold pedal half way rather than clutch out in neutral .

 

[drugekull]

how does putting it in neutral at a stop save the clutch compared to pushing in the pedal? when you push the clutch pedal, it is not engaged, therefore there is zero wear

yeah its not really about wearing the clutch plate but the presure plate springs will be under load eventually the presure plate will start to go and you get shudders and so on

its a miner difference but everything helps at the end

 

[Philip Foglar]

Yep! With a carb fed engine, coasting in neutral down a hill saves fuel, on a fuel injected engine it's the other way around - under closed throttle above I would think normal idle speed the fuel supply is cut, so zero fuel consumed. Modern diesels do this too, but then diesels use so little fuel when idling compared to petrols!

I also sit in neutral with my foot off the clutch and my hand off the gear lever when sitting at a robot - use the adjacent robot lights to judge when I need to get going. Trying, patiently to teach my Wife to do this too! :nonono:

 

[Sankekur]

Yup with a fuel injected motor freeing in gear the wheels are turning the engine over, and the the injectors are not fuelling so zero fuel consumption.

Have also heard in some cases that along with this the throttle is opened fully along with this to allow the engine to free with more ease.

 

[frikkieh]

how does putting it in neutral at a stop save the clutch compared to pushing in the pedal? when you push the clutch pedal, it is not engaged, therefore there is zero wear

The pressure plate and the thrust bearing should last longer if you don't put your foot on the clutch whilst waiting at the red light.
Waiting at a light you should shift to neutral and take you foot off the clutch pedal.

 

[Philip Foglar]

Yup with a fuel injected motor freeing in gear the wheels are turning the engine over, and the the injectors are not fuelling so zero fuel consumption.

Have also heard in some cases that along with this the throttle is opened fully along with this to allow the engine to free with more ease.

Interestingly the E46 (the 320i) seems to have less engine braking effect than the E90 330i. It's amazing to see the econometer sitting on zero while practically maintaining a speed on a somewhat "level" decline!! :rollsmile:

 

[Sankekur]

Yup it is pretty awesome :rollsmile:

 

[kabal]

how does putting it in neutral at a stop save the clutch compared to pushing in the pedal? when you push the clutch pedal, it is not engaged, therefore there is zero wear

The pressure plate and the thrust bearing should last longer if you don't put your foot on the clutch whilst waiting at the red light.
Waiting at a light you should shift to neutral and take you foot off the clutch pedal.

you could spin this around and say changing to neutral and then to first at a stop wears your syncos, and gearlever bushings :fencelook:

obviosuly i am changing to neutral at long stops.... I just thinking saying you do it to prevent wear is :fishwack: