Ticking over in "D"

[verytalldave]

Sat sitting in a traffic jam on the devils own highway to hell today made me think.
There was I, foot on brake and car in "D" for well over 10 minutes. Silly really. I wasn't thinking.
So how long before you would cause gearbox damage doing that?
Or wouldn't it ever get to that point?

 

[Bobby Dazzler]

By design the torque converter just slips (as it's a fluid coupling rather than direct drive) and so no damage. I guess it would heat up the fluid though. It would also place a bit more wear on the brakes.

 

[corned]

I don't think it's a case of x amount of time = y amount of damage, and it will be the TC rather than the gearbox which will suffer.

I believe it will be a temperature increase caused by the swirling ATF in the TC which will eventually cause ongoing problems. At standstill, half of the TC is stationary, like the rest of the geartrain, and the other half is rotating at engine speed. The fluid in the TC is being thrashed between the two parts and will inevitably get hotter as a result. Just how hot, and what consequences there may be, I cannot say. Other than to say that if it is habitual (I know this is not the case here, but I am just saying...) then something will give somewhere along the line. Can you 'cook' ATF?

When on the move, both parts of the TC are going to be moving, so the situation is not the same.

My business partner bought a Volvo S-something-or-other with an auto box, and was told not to keep it in D for long at lights, etc, etc. Now to me, that sounds more like a salesman attempting to defer an existing problem from coming to light, but that's just me. On the other hand, he could have been really conscientious and was simply offering sound motoring advice.

 

[corned]

Thanks, BD - I forgot that point. The practise of sitting with your foot on the brakes is the more likely to cause ongoing problems. Particularly if you have had a period of time before you came to a halt where you were giving the brakes a good workout. When you sit with the brakes applied, the hot discs cannot dissipate their heat, or rather, the part of the disc held under the pads cannot, and as the rest of the disc cools - but this bit doesn't - you can warp your discs as a result.

Guess how I know!

 

[Bobby Dazzler]

The common response to this sort of question is that there's more wear associated with shifting out of D than staying in it.

My rule of thumb...

Traffic lights, stay in D and on the foot brake.

Hold up, move to neutral and parking brake.

The latter is kinder to your foot and the eyes of the person behind you (if dark/wet/foggy).

 

[st4]

Sat sitting in a traffic jam on the devils own highway to hell today made me think.
There was I, foot on brake and car in "D" for well over 10 minutes. Silly really. I wasn't thinking.
So how long before you would cause gearbox damage doing that?
Or wouldn't it ever get to that point?

For a stop for any longer than 1 minute, turn off the engine. You'll save a lot in fuel.

 

[Rory]

For a stop for any longer than 1 minute, turn off the engine. You'll save a lot in fuel.

...but you'll get hot and sweaty.

 

[st4]

...but you'll get hot and sweaty.

Not a problem up here I can assure you. However where VTD lives they do have a summer of some description but a frugal man like me would get hot and sweaty just thinking about idling a car for 10 mins.

 

[bennesspipers]

Haha like it ***

 

[alanuk400]

My business partner bought a Volvo S-something-or-other with an auto box, and was told not to keep it in D for long at lights, etc, etc. Now to me, that sounds more like a salesman attempting to defer an existing problem from coming to light, but that's just me. On the other hand, he could have been really conscientious and was simply offering sound motoring advice.

I was told that when I had a E32 BMW 730. The box can be wrecked if left in neutral on tickover.

Alan

 

[LimitedSlip]

The cage/gear carrier assembly rotates when in neutral, which eventually must cause some wear, though it would take a lot of idling to be a real problem unless in a "vulnerable" design I would think.

Idling in gear is as described by previous posters, but also uses more fuel than in neutral as the engine must produce enough power to not stall against the load of maintaining the oil slippage in the torque converter, hence the extra heat.

In Park, the converter is drained/relieved so the turbine/driven section will not rotate: no gearbox assembly movement, engine idling virtually freely so less fuel used.

The disadvantage on some gearboxes (more pronounced in older cars nowadays) is the slower engagement back into gear from Park.

 

[verytalldave]

Thanks to to all.
Seems to be rule of thumb - OK at the traffic lights, but any longer then go into "P".......

 

[VB123]

I'd be more worried about melting the brake lights......god knows, they like doing that!

 

[Bobby Dazzler]

I personally prefer N than P. Our Omega once got stuck in P in a queue at thge McDonalds Drive-Thru - one with high-sided kerbs either side of the Drive-Thru lane. Not a great place to be stuck.

 

[jaymanek]

Going all the way into P just confuses people behind too as your reverse lights blink..

 

[219]

I'd be more worried about melting the brake lights......god knows, they like doing that!

I've never suffered that , but since I recently rebuilt my brakes , and now have an excellent handbrake ( unusual for a Merc ) I now tend , for shorter stops , to leave the car in drive , but with handbrake rather than footbrake .

 

[ceejay]

I recall reading some while ago that one of the hot weather tests carried out on new cars was to drive the car up to a wall in a hot climate, and leave it idling in drive all day!

 

[219]

Rudi Uhlenhaut's famous hot weather test was to load a kilo of butter into the boot and go for a day's drive into the mountains , after which the butter should not have melted , otherwise - FAIL !

One less good example was my 5 speed manual 280E which used to regularly get an airlock in the clutch hydraulics because the pipe went too close to the exhaust and the puny heat shield was just not up to it - the minor detail that I used to get the car 'well warmed up' had nothing to do with it

 

[LimitedSlip]

Going all the way into P just confuses people behind too as your reverse lights blink..

That is a point jaymanek, and something I've long thought could've been easily addressed with modern electronic controls, a delay of a second or so after selection of reverse until the lights come on.

Another like this is the brake light thing: why don't they go off after several seconds of being stationary in an automatic car with the brake pedal depressed? Would stop a lot of dazzle and also the fading of certain lenses.

 

[lynall]

I was told that when I had a E32 BMW 730. The box can be wrecked if left in neutral on tickover.

Alan

I to remember the bmw boxs doing this, of course mbs dont have gearbox probs



Lynall