Coasting in Neutral Does Not Save Gas: Claim Check

I have been saying this for years but nobody wants to believe me. I try to get people who don't believe to realize it is throttle position that regulates fuel economy more than engine RPM.

I drive a manual truck and always monitor my fuel consumption when I fill up. I may not have the most accurate method because I cannot fill it to the exact quantity every time but I would notice a trend if there was a difference. I used to just put the clutch to the floor and coast to a stop, now I always use engine brake (consuming some clutch material) by downshifting through the gears as I slow. I have not noticed a difference in my fuel economy either way.

Drew

@ Drew, your comment here is also one that has been falling on deaf ears for me

"I have been saying this for years but nobody wants to believe me. I try to get people who don't believe to realize it is throttle position that regulates fuel economy more than engine RPM."

I say leave the doubter to it

Mostly I do...unless I am feeling confrontational and want an argument.

Drew

Well I've used coasting over the last 30k km- my mpg has gone from 38 to 48 genuine- the only thing is to turn the motor off !- & coast in neutral!(1978 Isusu 1.6l car 5 spd manual). And you are constantly watching for idiots ahead & behind- including coppers!. The vehicle has done 727k km & is not babied- just treated sensibly & maintenance done as needed. That said, I drive mainly in backwoods areas- I don't like the modern stressed out, drugged up gotta get their yesterday drivers!- prevalent in urban areas!. Cheers!.

Really ? Well, you haven't considered the millions of carbureted models in your instrumented calculations; where no pulse width can be measured. I have experienced many, many times the gas-sucking effect of coasting downhill while the transmission is engaged, it revs up your engine above the ≈1kRPM iddling speed, thus actually sucking gas thru the carb.

This is very noticeable when I'm running out of gas, if I leave the clutch engaged, I won't have enough gas to reach the next gas station up-hill. If I coast in neutral, I'll have enough gas to get there.

How come I have experienced this so often? Simple: My old CJ5 doesn't have a fuel level indicator; I recently replaced it with one made in China, but it worn out in a week (resistor winding opened). Now I carry a gerry tank, but that's a whole other story.

Yahlasit

I think there is something to coasting with a carbureted engine, especially with those SU types. But the article is from an American Magazine and the author didn't know much about much else. I don't know as much about American Carbs because I never worked on one; I did however work on my old Mini in England when the military sent me there.

Neil Kwyrer above has a dangerous situation described where it appears he shuts the engine down while driving downhill. This may not be a big deal for him but many people would run into problems with that situation. One or two applications of the brakes depletes the advantage of power brakes. The resulting panic might send an inexperienced driver over a cliff. I would only suggest it if the vehicle had been redesigned to shut off the engine when it isn't needed; but that would take alot of modification.

Drew

yep, i,too am one that hits neutral and kills the engine for a "free ride" downhill. You have to be very coordinated and careful, because you have only 1 or 2 brake taps before you loose power/vacume assisted braking, and power steering is gone as soon as you turn off the key. My pickup truck ALWAYS restarts with one quick turn on the key, although i still drive like it may not start that time. I drive a 93 dakota, with comp controled injectors, so my break even point is less than 5 seconds. Normal driving gives me about 220 miles to the fillup, killing the engine downhill and at traffic lights brings it up over 300 miles per tank. I do a lot of intown driving, so killing the engine at lights really saves quite a bit. I have a lifetime warranty starter, and use revived junk batteries (yahoo batteryconversion group speks) under the hood, so, before anyone thinks i am actually loosing money by using the batteries and starter more, i aint.

Good day like minded- I coast in neutral with engine turned off- when speed has dropped from may'be 80km/hr to 20km/hr- clutch in, engage 4 th gear, turn ignition on, let out clutch smoothly,accelerate smoothly again- cycle repeats- don't need big hill- any decline ahead can be milked- even 1/2 km is worth it. No power steering- has carby- vac assist brakes- but man braking quite ok, as earlier version did not have vac assist(yes I own one). Sure at first seems to take longer to get anywhere- but get used to it- & big benefit of being able to look around at passing scenery as car coasts. YoHoHO!.

Great Wiki article, thanks.

It calls my attention that the original poster, who is concerned about fuel economy, might not be as much about safety; at the end he seems to be ok if you turn off the engine, but for God's sake, don't coast in neutral! ( He's been telling us this for years!)

Yahlasit

Though, I admit it's unsafe to coast in neutral to a stop within traffic, you might need to accelerate quickly to avoid a crash.

Yahlasit

This may be a little off the topic. I noticed in Japan that everyone turns off their lights when they stop at a traffic light. I notice the lights, but can't tell if they also turn off the engine.

Many modern fuel injected engines will stop the flow of fuel to the engine when the throttle is closed and the engine RPM is above aproximately 1800 RPM if the vehicle has a manual transmission. So you get the best fuel economy when braking just by downshifting to keep engine speed above 1800 with the throttle closed. A benefit of this is that you still will have your power steering and power brakes working because the engine braking keeps the engine turning over. If you coast with the engine idling your engine still uses fuel. This is a simple system that has been in use on VWs with Bosch FI systems since 1985. Coasting with the engine off is just as fuel efficient both as stated earlier, you will loose power assists and the ability to quickly accelerate.