Driving & Driving Test Tips: Coasting in Neutral to Save Gas, minor extent, engine brakes

Question
Don,

This is NOT a safety question as I know you need significantly more time to stop in neutral than in gear.
Question:  For over 20 years, when going down mild grades or even upon coming up on stop lights, I will pop my car out of gear to not only save on gas but to a minor extent save on engine wear and tear as the car is just idling when coasting.  I understand the trade-offs are longer braking distance, again I am not asking from a safety perspective though, increase brake wear and to a lesser extent greater clutch use.  I do this because I believe I save more in gas and engine wear than break pad/clutch pad replacement costs.  Do you agree?

Answer
I will agree with this reservation.  Any savings in fuel/engine wear is minimal since as you slow down, the throttle is closed and you aren't using as much gas at 40mph slowing down, as you are at 40 mph cruising.  So the savings may not be as much as you think.  The savings will be more with a manual transmission car than an automatic, since you can go close to idle with a manual transmission car, where an automatic, even with the torque converter will hold rpm's up somewhat more.

But with modern manual transmisssion cars, at least the ones I have dealt with, the computer won't let the car go to regular idle till speed drops almost to nothing.  This has something to do with emmissions.  Watch your idle on most modern cars, and as you coast to a stop, idle will stay up a few hundred rpm till almost stopped.

Also, I will say this that in many states, coasting out of gear is illegal....hard to enforce, but there are reasons, since if you have an emergency, you are no longer in the mode you are most used to.

As for the brakes, it makes very little difference, since the engine on modern cars doesn't apply the braking force that they did on older cars.  Again, this has something to do with emissions and computer control of the engine.

Brakes are designed to do all the work in any case, so I doubt the life of the brakes is effected more than 5-10% if that much.

You don't say what you do when you go out of gear, but with a manual transmission, you should shift to neutral and not keep your foot on the clutch, that causes more wear on the throwout bearing.  Most clutches die from bearing wear than actually wearing out the clutch itself.  The bearing can go bad, or it can eat through the clutch pressure plate fingers.

Overall, I think your gas savings probably are about equal to the increased brake maintenance, so keep doing this if it makes you feel good, but it would probably take some top quality scientific methods to prove any savings one way or the other.

Don