Shifting into neutral while at long stops? Any benefit?

[Busbin]

I occasionally ride with a friend (BMW guy) who always shifts his automatic transmission into neutral while sitting at any long stop light. He seems to think that this will extend his transmission life by reducing wear, heat build-up, and so forth. Is there any credence to this notion? Or will this do more harm than good?

Jim in the NC mountains

[Q45tech]

Older BMW AT were prone to increased failure in neutral because the pump stopped running but they kinda fixed that.

Other than the shift shock when you return to drive probably equal chances against/for.

The rpm will go up but the fuel usage per second will decline since engine dosn't have to fight TC to slip..........it has to make less power in neutral than drive.

I would think 4-5 minutes would be the pivot point when neutral night be a small advange.

[seldomseen]

No benefit will be gained from this practice. As long as your friend doesn't beat the car and keeps the transmission fluid up to snuff he should be fine. Unless crappy transmissions is a common problem with the car he has---then he's just effed.

[elwesso]

I would think for something you know you're going to be parked for a long time is going to be a good idea (like a train) or something, but unless you're gridlocked shifting in and out of drive is not going to good for it..

[oldmako]

How about in stop and go traffic? I try to keep it in first and just keep rolling. My thought is why use all those shifts when you're really going nowhere fast??

[Victor]

I just did a web search on the question and got mixed views. Most said it didn't help much, in fact could put more wear and tear on an automatic transmission and the driveshaft. But the torque converter does run cooler in neutral so you may want to shift to neutral on a very hot day. In a manual transmission car you definitely should shift into neutral when stopped to prevent wear on the throwout bearing. I usually shift to neutral at long stops because I almost always run my air conditioner and figure I might as well let most of the engines power be used to run the air conditioner instead of wasted heating up the torque converter. Several articles said in Britain by law you have to shift to neutral while stopped. Some articles recommended shifting to neutral while going downhill to save gas, but that could be a safety hazard if you suddenly needed power, and could burn out your brakes on a really steep hill without engine braking.

[bobbuzz]

I think you ought to write that up as fact, then send it to Myth Busters!

Bob

[Skibane]

At idle speed, my Q is capable of creeping up a pretty decent incline, if I take my foot off the brake. How many horsepower does it take to almost immediately get a 4000 pound vehicle moving up an incline? My guess is several.

When the vehicle isn't moving, most of that several horsepower is instead being dissipated as heat inside the torque converter. If you dissipate 2 horsepower as heat, you get around 1500 watts, which is around 5,000 BTUs - which is NOT an insignificant amount of heat.