How much gas can you save by putting your car in neutral during some points of driving?

Question

I was in the car with some one the other day, and he put it in neutral right before going down a hill to save gas. The RPMs lowers when you put it in neutral, so you save a bit of gas until you need to accelerate to stay at the speed limit. How much gas can you save doing this? I guess it depends on where you live. Obviously if your path contains a lot of down hills, it helps, while if your path contains mostly up hills, there will be very few times when it can be done. The area I live in is kinda in the middle in terms of "hilliness". But anyways, how much gas do you think I can save from putting the car in neutral right before going down a hill?

Answer 1

I don't think it is worth it.

Answer 2

If it's a modern car with fuel injection and engine management (i.e. like all models sold in the UK, Europe and Japan for at least the last six years) then it uses MORE fuel to coast with the engine idling in neutral.

Modern systems only squirt in the go-juice when it's needed and when an engine is slowing down whilst still in gear (a.k.a. "engine braking") the engine management system instructs the fuel injectors not to feed any fuel at all to the engine. On these systems the engine management will continue to feed fuel to the engine when in neutral as it assumes the car is waiting whilst stationary like at a junction or traffic lights.

On older conventional cars with mechanical fuel pumps and carburettors an overrunning engine still gets fed with some fuel, but the carburettor float chamber should restrict most of it.

Any overflow is either fed back to the fuel tank, dumped directly from the carburettor (like on a Citroen 2cv/Dyane/Ami) or gets fed through the engine anyway to end up as unburnt hydrocarbons in the exhaust. If a catalytic converter is fitted the unburnt hydrocarbons are converted to water and CO2 and if not they just add to pollution.

So on an older car, the amount of fuel saved in neutral can vary between very little or a fair bit, depending on the fuel system design and the type of driving but in my experience I used to save about 10%.  Be cautious though as in some countries coasting in neutral is illegal as it's regarded as leaving the driver without full car control, but it would be difficult to prove.

Answer 3

If you can save a little each day, over the period of a month or a year it can add up to a lot.  There are also different techniques you can use to save gas, called 'hypermiling'.  Check this site out http://en.wikipedia.org/wiki/Hypermiling

Answer 4

Not enough for it to be worth the damage it does to the transmission.  Drive without cruise control and just let your foot off the accelerator when going down the hills and you will accomplish the same thing without any damage being done.