: Tranny cooling question



carguy16
06-07-05, 06:43 PM
I have a question, why in park or neutral, why does the tranny oil cooler lines get really hot?

If I get done driving, and touch them, they are luke warm, but when parked/idling they get hot after you shut the car down and feel them. Why is this?

Another mystery...

HotRodSaint
06-07-05, 10:27 PM
Another mystery...

No airflow through the 'radiator' when you are stopped?

carguy16
06-07-05, 11:39 PM
Yes, but, the car could sit there for an hour, you touch the lines and they are cool. You start the car up, and have it in neutral or park, they heat up fast, does heat permiate through the engine, or what?
No airflow through the 'radiator' when you are stopped?

HotRodSaint
06-09-05, 12:19 PM
Yes, but, the car could sit there for an hour, you touch the lines and they are cool. You start the car up, and have it in neutral or park, they heat up fast, does heat permiate through the engine, or what?

Maybe the 'stagnant' fluid in the lines cool down, but when you run the car the hot fluid flows into the lines?

N0DIH
06-09-05, 01:55 PM
I would agree. There is a thermostat in the trans, so fluid isn't always cooled in the cooler. It is like the engine, maintains a certain temp, mainly for fuel economy, but also for lubricity. Too cold fluid and trans may not perform properly. BBob can likely fill in more on that.

FASSTWOOD
06-12-05, 12:36 AM
I never heard os a thermostat in a tranny... you learn something new everyday!!!

ocjmakaveli
06-12-05, 03:41 AM
I never heard os a thermostat in a tranny... you learn something new everyday!!!

its not a thermostat just a fail safe thermometer which only turns on once the trans go over temp and its supposed to eliminate the OD so that the tranny will avoid overheating etc. but I've read many threads and this doesn't work too well most of the time.

ocjmakaveli
06-12-05, 03:44 AM
Yes, but, the car could sit there for an hour, you touch the lines and they are cool. You start the car up, and have it in neutral or park, they heat up fast, does heat permiate through the engine, or what?
i would say this is the safest bet trust me if you were touching the engine as does the trans then you would get very hot very quickly seeing as how the engine is at about 200 degrees its very easy for standstill trans fluid to get very hot while so close to the engine at all times.

my second best bet would be since the torque converter works at all times that might cause the rise in temperature since their is no cooling while the car is stopped etc.

either way this is nothing to worry about.

N0DIH
06-12-05, 04:19 PM
They have it now on the "modern" trans that do not circulate fluid to the cooler until it gets over a certain temp. The old THM350's and 400's didn't, but the newer ones do. I learned this the hard way on a A4LD I was trying to swap fluid on in the winter, pulled the cooler lines and nada, nothing, hardly a drop came out. Do some more research and yup, thermostat.

After digging in my FSM, it looks to be controlled by the Pressure Control Assy, the temp is controlled by the PCM. If you follow the cooler line flow, the return line goes to the control assy, which can restrict flow as needed to maintain temp based on the temp sensor.

The flow charts do not specically show a cold operation. The older trans have a thermostat, the newer ones eliminate that part and let the PCM control it.


its not a thermostat just a fail safe thermometer which only turns on once the trans go over temp and its supposed to eliminate the OD so that the tranny will avoid overheating etc. but I've read many threads and this doesn't work too well most of the time.