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Coasting with automatic transmission

Do you think shifting an automatic from drive to neutral and back is harmful to the transmission? I often do it when coasting down hills at high speeds or approaching toll booths/off ramps to keep the engine from running at high RPMs and burning unnecessary fuel when decelerating.

What you are doing is:

Illegal
Unnecessary
Not fuel efficient
Potentially damaging to the transmission

How old is your car? Most cars from the 90’s and newer cut off all fuel to the engine when you’re foot is off the gas, engine speed is above idle, and the transmission is in gear. So, no you are not hurting your transmission, but you are causing yourself more fuel consumption, not less.

Great, that answers my question. Thank you. I have a two year old car so I guess the engine would shut off.

I’m curious, where is this illegal? How do they determine that and why? Thanks.

I’m pretty sure all 50 states have a rule against coasting in neutral, though obviously it’d be pretty tough for them to actually catch you doing it.

I have a two year old car so I guess the engine would shut off.

Almost certainly.

The reason why this practice is illegal in every state with which I am familiar is that you rob yourself of compression braking when you put the transmission into neutral on a downgrade. The result is more brake wear and less stopping ability.

As GreasyJack stated, it would be damn hard for anyone to prove that you were doing this, but hopefully good judgment will prevail after you have read all of the posts indicating that your current practice is wrong.

I believe the law was created for truck drivers. Their manual transmissions don’t have synchronizers, making it difficult to shift from neurtal into a gear. In order to shift into gear, the driver must manually synchronize the speed of the engine and the speed of the transmission, which isn’t easy if you are coasting. If a loaded truck gains enough speed coasting downhill, the driver may not be able to get it back in gear and may lose control or he may overheat the brakes trying to stop.

It is really about keeping control of your vehicle. If it is in gear going down a hill, you have more control than if it is coasting. That is why it is unsafe.

[I often do it when coasting down hills at high speeds or approaching toll booths/off ramps to keep the engine from running at high RPMs and burning unnecessary fuel when decelerating.]

Bad idea. Keep the trans in a lower gear when going down a hill. Otherwise you just heat up your brakes. That’s bad. Also in the event you need quick acceleration for whatever reason, you go from 2WD to 0WD. That’s bad.

As others have said “freewheeling” is illegal. If it was a manual transmission it would be different because you have to shift to neutral to shift back into first anyway so why not cruise to a stop in neutral, but the automatic keeps you from having to bother with it.

“I believe the law was created for truck drivers. Their manual transmissions don’t have synchronizers, making it difficult to shift from neurtal into a gear.”

I would tend to agree with this statement (w/o any research myself). There are isolated instances where free wheeling might be an advantage and I don’t think the law was intended for the “normal” passenger car.

Normally, engine braking is such an important part in maintaining vehicle control, IMO it should be part of normal driving provedures…reaalizing there will always be exceptions.

I’d hate to think that if I still had my old two stroke SAAB, I would be breaking the law each time I let let up on the accelerator with the auto free wheeling device engaged.

I agree: where is it illegal? An online perusal of the PA motor vehicle code (Title 75, part III (Operation of Vehicles)) indicates no statute explicitly prohibiting ops. in neutral.

Hey, is anyone out there old enough to remember the overdrive in the 1940 and 50s cars. It was coasting while in gear. Just don’t use it in city traffic or you might end up with some car on your hood as an ornament.

Well it certainly won’t save any fuel and putting a trans in neutral and shifting back to drive will take a long time to tear it up but certainly won’t do it any good.

There is really no point to coast in neutral with an auto transmission. The torque converter acts like a bicycle gearing system, where torque can only be applied in one direction. This means the auto trans is practically in neutral already when you let of the gas to coast to a stop.

The only exception to this is when you turn off overdrive, or put the transmission in a lower gear such as 2nd or 1st. In these cases, the lock-up clutch engages for the purpose of engine braking. Still, I doubt you’ll be burning unnecessary fuel when doing this.

Neutral on an auto transmission is mainly used for prolonged idling (e.g. drive-thru that hasn’t moved for 10-minutes), or to start the vehicle. It wasn’t really designed for coasting.

if I knew i was going to have to wait for more than 2 minutes in a drive thru, I’d just park the car and go in

I believe a torque converter works both ways but doesn’t have as much drag if the car is pushing the engine. Also I don’t think any converter clutch locks up in 1st or 2nd gear. I have a GM and a Chrysler both and if overdrive is turned off the converter will lock up in 3rd. However when you let up on the gas or touch the brakes on the GM the clutch will release. (it’s one way). On the Dodge, it doesn’t release.
But I don’t think it is a good idea to shift to neutral when coasting or stopping.

So you would rather pay that extra $.05 you think you might save in gas every three months toward the extra brake job of $500 plus during the life of the car…hmmm.

mrm, I have had 2 and still have 1 vehicle with overdrive, and they did not lock up in 1st or second. Also I think the torque converter works both ways however not as much when you let off the gas. (car pushing the engine). I also know this post is over 30 days old so probably no one will read this.