driving in neutral to save fuel

hothothot_3

hundredk wrote: »

This is more efficient than coasting in neutral but you need a manual car.

Thanks hundredk, I actually used to drive like this as my normal driving style, much to the annoyance at times of people behind, but it is indeed a great way to save petrol.

Ive just checked my new cars' manual (Vauxhall automatic), and it states the following;

Overrun
The fuel supply is automatically shut off
during overrun, e.g. when the vehicle is
being driven down long gradients or when
braking. To enable the overrun cut-off to
take effect, do not accelerate during
overrun and, if in manual transmission
mode, do not de-clutch. To prevent
damage to the cata lytic converter, overrun
cut-off is temporarily deactivated when the
cataly tic converter temperature is high.

So whoever was talking about this cut off thing, it seems that putting the selector to N is a waste of time, just take foot off gas and the car does its stuff all by itself. Excellent. :cool:

cajef

dixie_dean wrote: »

Crapped myself when I had to break and found the breaks stop working after a while with no engine on! I have a ford focus - don't know if this is the same for all cars.

The brakes did not stop working, most modern cars have servo assisted brakes without the engine running you just lost the vacuum to the brake servo, consequently you need leg muscles like Mr. Universe to press the brake pedal hard enough to stop the car.:D

Wig

dixie_dean wrote: »

On a slightly different note, I did actually turn the engine off whilst coasting down a hill as was VERY low on petrol (and don't know much about cars). Crapped myself when I had to break and found the breaks stop working after a while with no engine on! I have a ford focus - don't know if this is the same for all cars.

You also run the risk of the steering lock coming on, unless you reset the ignition key back to the 'ignition on' position. That would have been curtains for you.

cyclonebri1

Wig wrote: »

Except as I have shown, Vauxhall says not all cars have this feature, and no-one has yet been able to show that all petrol/diesel cars after a certain year has this feature (contrary to what vauxhall says) no-one says how many seconds it takes before fuel is shut off because no-one knows.

And even on cars with this feature, they will slow down quicker in gear and require accelerator pedal to be used to bring them back up to speed, thus using quite a bit of fuel over the same distance, compared to the car idling with "clutch in" using very little fuel and coasting along happily with very little resistance (by comparison) to slow the vehicle down.

Sorry Wig, but that is rubbish. All cars on fuel injection since at the latest 1983 do shut off all fuel on the overun. As soon as the throttle potentiometer is released, ie the throttle closes, asuming revs over the threshold I mentioned, there is no more wasted energy.

Plus, you and me must be sad gits indeed arguing this point on a christmas eve, MERRY XMAS, :xmastree::xmassign::santa2:

Wig

cyclonebri1 wrote: »

Sorry Wig, but that is rubbish. All cars on fuel injection since at the latest 1983 do shut off all fuel on the overun. As soon as the throttle potentiometer is released, ie the throttle closes, asuming revs over the threshold I mentioned, there is no more wasted energy.

Plus, you and me must be sad gits indeed arguing this point on a christmas eve, MERRY XMAS, :xmastree::xmassign::santa2:

And a :xmassign: to you too. -I'm in the middle of watching last weeks Merlin on iplayer- but iplayer wasn't loading the next episode for me so I came back here.

We have had this discussion before and I quoted my vauxhall manual which says 'overrun' was a feature not present on all models. Until someone can explain that, and show that it is definately present on most if not all cars after a certain date.... I will continue to believe that it may not be present on any car I drive.

However having said that, even if it is on all cars, my point about the car slowing down if left in gear is valid, you will have to apply accelerator a lot more than if you were just freewheeling along, hence more fuel is used overall.


Back to Merlin.....

hundredk

hothothot wrote: »

Thanks hundredk, I actually used to drive like this as my normal driving style, much to the annoyance at times of people behind, but it is indeed a great way to save petrol.

Ive just checked my new cars' manual (Vauxhall automatic), and it states the following;

Overrun
The fuel supply is automatically shut off
during overrun, e.g. when the vehicle is
being driven down long gradients or when
braking. To enable the overrun cut-off to
take effect, do not accelerate during
overrun and, if in manual transmission
mode, do not de-clutch. To prevent
damage to the cata lytic converter, overrun
cut-off is temporarily deactivated when the
cataly tic converter temperature is high.

So whoever was talking about this cut off thing, it seems that putting the selector to N is a waste of time, just take foot off gas and the car does its stuff all by itself. Excellent. :cool:

Many modern cars now have fuel computers and an easy way to check if the overrun has cut off fuel is to set to instantaneous consumption. If the display max's out (often 99.9 or 999.9mpg) you are using no fuel. It is suprising how far and long you can travel on the momemntum gained from a short burst of acceleration.

Wig

hundredk wrote: »

Many modern cars now have fuel computers and an easy way to check if the overrun has cut off fuel is to set to instantaneous consumption. If the display max's out (often 99.9 or 999.9mpg) you are using no fuel. It is suprising how far and long you can travel on the momemntum gained from a short burst of acceleration.

Read post #35

jazabelle

dixie_dean wrote: »

On a slightly different note, I did actually turn the engine off whilst coasting down a hill as was VERY low on petrol (and don't know much about cars). Crapped myself when I had to break and found the breaks stop working after a while with no engine on! I have a ford focus - don't know if this is the same for all cars.

I did that! My car stalled and I was going down a hill, so thought oh well - will save some fuel and leave the engine off as I'm rolling anyway. The bleeding brakes stopped working and I almost had a heart attack! Luckily managed to get the engine back on a stop in time. Would not have liked to explain that one to my insurance company! Stupid me will not be doing that again.

hundredk

Wig wrote: »

Recently driving a punto with a fuel use display, I experimented
Driving in gear with supposed overrun able to kick in if it it exists on the vehicle
fuel display eventually reached 141.3mpg and stayed there
Driving with my clutch down fuel display eventually reached 141.3mpg and stayed there

So unfortunately the exercise proved nothing. The only difference was, as always, driving in gear the car slowed down quicker and had to be helped along earlier (thus using more fuel).

The display max's out at 141.3mpg ( a strange figure but probably a technical reason for it). It is quite easy to achieve more than 141.3mpg by coasting in neutral, so lets say you were doing 200mpg, the display would show it's max 141.3mpg. If you were in gear on overrun you would be doing infinite mpg but the display would still show it's max figure. On most models, usually 99.9mpg or 999.9mpg on the display is indicative of no fuel used in gear on overrun.

Wig

hundredk wrote: »

The display max's out at 141.3mpg ( a strange figure but probably a technical reason for it). It is quite easy to achieve more than 141.3mpg by coasting in neutral, so lets say you were doing 200mpg, the display would show it's max 141.3mpg. If you were in gear on overrun you would be doing infinite mpg but the display would still show it's max figure. On most models, usually 99.9mpg or 999.9mpg on the display is indicative of no fuel used in gear on overrun.

You're assuming the car has overrun (see post #46)

Assuming it does have overrun you're ignoring the fact that you coast further and faster freewheeling than you do on overrun, it is entirely possible that the extra fuel you use when using overrun means that overall you use less when freewheeling.