I recently read some of the threads on this site about a variety of fuel saving measures that people employ in a bid to go a bit further on each tank full. This is something that is particularly appropriate these days, when a typical tank of fuel is costing between £5 and £10 more than it did before the end of last year!
One of the methods that was being discussed was the ‘keep it in gear at all times’ method as opposed to the ‘put it in neutral and let it coast’ routine. I’ve previously always naturally, by habit if nothing else, let the car coast along a road or down a hill when I’m not accelerating, even though I’m aware that it’s probably a better driving technique to always keep it in gear, even when decelerating. The general consensus on this site seems to be that the ‘keep it in gear’ method is always more fuel efficient too. Someone wrote that it was only the old carburettor engines that might save a bit of fuel by coasting, as it’s the momentum in newer injection engines that actually keeps the revs up (or something like that!). Jeremy Clarkson has also, at least twice now, preached this to viewers of Top Gear (even ridiculously as an alternative to actually using the foot brake!).
So, I thought I’d make a determined effort to try the ‘keep it in gear’ driving method to see exactly how much fuel I’d save on a typical tanks full. My 1.4 TDi (75bhp) usually returns late 40s/early 50s in terms of MPG with a combination of town and motorway driving usually on each tank full. I was somewhat disappointed however, to say the least, when my first full tank of juice returned only 43.92 MPG.
WTF(!) was my first reaction!
I then decided to hell with this ‘leave it in gear’ business and went back to full on coasting in neutral whenever and wherever I could. On a personal note, I don’t think it’s any less safe to drive this way, but I know others will argue against this no matter what I say!
After refilling this time, I was pleased my little motor had returned a more sensible figure of 51.70 MPG using the same driving style. But, in the name of science, I decided to give this experiment another go. So again, it was a tank full of keeping it in gear driving, followed by another tank full of coasting. The MPGs were 46.96 and 49.26 respectively.
My driving style over the four full tanks of diesel has been deliberately consistent, although if anything, for the last tank full of coasting driving (the tank full that returned 49.36 MPG), my driving has noticeably been a little more rushed due to being a bit more stressed recently- but I digress!
Of course, there will always be other minor factors that will affect MPG which my experiment has not taken account of, BUT, and this is a big BUT, you can see for yourself, that my ‘leave it in neutral and coast’ method seems to have returned a better MPG on both occasions. OK, so I should really conduct this experiment over a full year or so to get a better understanding of exactly which method saves more fuel, however I am more than satisfied with the results that I have seen so far, and will probably continue to use my existing ‘coast in neutral’ driving style, purely on what I have witnessed.
I think the ‘coast in neutral’ method works for several reasons:
• When you are in gear but not accelerating, the engine naturally wants to slow down, however if you are not ready to decelerate, then you will always have to apply more throttle, thus using more fuel. This is particularly appropriate on relatively flat roads where, when coasting, the momentum of the car will carry you along.
• When decelerating in gear, the engine’s RPM will always be greater. I’m no mechanical geek, but surely at a higher RPM, the engine will always burn more fuel than at tick-over. There will always need to be fuel in the combustion chamber?? Am I wrong?
• When coasting, and at speed, the air flow will be helping to cool the engine down easier than if the engine was still rotating at 2.5k or 3k RPM, perhaps even more. At tick-over, the engine is having to work less and will be therefore using less fuel.
There will be those who are reading this thread who will undoubtedly argue against the case for driving in neutral and coasting, and to those people, I don’t disagree with you in the slightest. All I am doing in presenting the facts - facts which I thought that a few others may be interested in hearing. If you don’t believe me, try it yourself. Give the experiment a go and then tell me I’m wrong. Remember to not alter your driving style though so that your results are fair and measured.
It will be interesting to see if anyone agrees with me! Happy experimenting…
One of the methods that was being discussed was the ‘keep it in gear at all times’ method as opposed to the ‘put it in neutral and let it coast’ routine. I’ve previously always naturally, by habit if nothing else, let the car coast along a road or down a hill when I’m not accelerating, even though I’m aware that it’s probably a better driving technique to always keep it in gear, even when decelerating. The general consensus on this site seems to be that the ‘keep it in gear’ method is always more fuel efficient too. Someone wrote that it was only the old carburettor engines that might save a bit of fuel by coasting, as it’s the momentum in newer injection engines that actually keeps the revs up (or something like that!). Jeremy Clarkson has also, at least twice now, preached this to viewers of Top Gear (even ridiculously as an alternative to actually using the foot brake!).
So, I thought I’d make a determined effort to try the ‘keep it in gear’ driving method to see exactly how much fuel I’d save on a typical tanks full. My 1.4 TDi (75bhp) usually returns late 40s/early 50s in terms of MPG with a combination of town and motorway driving usually on each tank full. I was somewhat disappointed however, to say the least, when my first full tank of juice returned only 43.92 MPG.
WTF(!) was my first reaction!
I then decided to hell with this ‘leave it in gear’ business and went back to full on coasting in neutral whenever and wherever I could. On a personal note, I don’t think it’s any less safe to drive this way, but I know others will argue against this no matter what I say!
After refilling this time, I was pleased my little motor had returned a more sensible figure of 51.70 MPG using the same driving style. But, in the name of science, I decided to give this experiment another go. So again, it was a tank full of keeping it in gear driving, followed by another tank full of coasting. The MPGs were 46.96 and 49.26 respectively.
My driving style over the four full tanks of diesel has been deliberately consistent, although if anything, for the last tank full of coasting driving (the tank full that returned 49.36 MPG), my driving has noticeably been a little more rushed due to being a bit more stressed recently- but I digress!
Of course, there will always be other minor factors that will affect MPG which my experiment has not taken account of, BUT, and this is a big BUT, you can see for yourself, that my ‘leave it in neutral and coast’ method seems to have returned a better MPG on both occasions. OK, so I should really conduct this experiment over a full year or so to get a better understanding of exactly which method saves more fuel, however I am more than satisfied with the results that I have seen so far, and will probably continue to use my existing ‘coast in neutral’ driving style, purely on what I have witnessed.
I think the ‘coast in neutral’ method works for several reasons:
• When you are in gear but not accelerating, the engine naturally wants to slow down, however if you are not ready to decelerate, then you will always have to apply more throttle, thus using more fuel. This is particularly appropriate on relatively flat roads where, when coasting, the momentum of the car will carry you along.
• When decelerating in gear, the engine’s RPM will always be greater. I’m no mechanical geek, but surely at a higher RPM, the engine will always burn more fuel than at tick-over. There will always need to be fuel in the combustion chamber?? Am I wrong?
• When coasting, and at speed, the air flow will be helping to cool the engine down easier than if the engine was still rotating at 2.5k or 3k RPM, perhaps even more. At tick-over, the engine is having to work less and will be therefore using less fuel.
There will be those who are reading this thread who will undoubtedly argue against the case for driving in neutral and coasting, and to those people, I don’t disagree with you in the slightest. All I am doing in presenting the facts - facts which I thought that a few others may be interested in hearing. If you don’t believe me, try it yourself. Give the experiment a go and then tell me I’m wrong. Remember to not alter your driving style though so that your results are fair and measured.
It will be interesting to see if anyone agrees with me! Happy experimenting…