Thread: TDI Auto transmission overheating

Now that the box has been rebuilt and my bank balance is 4k lighter I'm keen to do what I can to keep temps down so have fitted an electronic sensor on the transmission line feeding the cooler.
Interesting that while driving at freeway speeds on the flat the temps sits around 50c, temps rise suddenly when not able to acheive lock up speeds such as up hills and as soon as lock up is reached the temps drops about 1/2 degree per second & can drop from 90c to 50c in a minute or two. I can't understand how the temp can drop so quickly and its almost like the cooler is doing nothing until lock up is reached.
Others have mentioned that the pressure increase's during lock-up so maybe the fluid gets to the cooler quicker, it was also mentioned that the fluid pumps in the opposite direction during lock-up which could mean the cooler fluid in the pan is sent back through the cooler and that explains the drop in temp. Also possible that because clutches are not working during lock-up there is less friction and heat but I would have thought temps would not drop so quickly in this case. Does anyone know what actually happens during lock-up that would explain such a rapid drop in fluid temperatures?
Anyways the good news is since the rebuild and synthetic fluid the temp light has not come on (same hills etc) and the max recorded temp has been 107c on a very steep climb off road pulling a 1200kg trailer. I would still like to keep temps down below 100c however so have ordered a P38 cooler from the UK after the valuable feedback on this thread.

Cheers
Mark
97 Disco TDI

your auto demistified.


The Grey Box of EVIL.. (aka autotransmission)

post 30 covers the TC.

as a rough rule auto fluids are good up to 160 degrees for prolonged use but derates very quickly over that temp.

in a nutshell..

when you hit the TC lockup you are driving the vehicle with a mechanical coupling from the engine to the gearbox, when your not locked up its driven on a hydraulic coupling.

best way to get a hill with the ZF auto? kick it back out of drive into 3, (put it in sport mode if its the electronic version) and build up some speed then ease of just a touch to allow the TC to lockup (if it hasnt already) then gently apply the power again to keep the momentum up.

Originally Posted by Blknight.aus

best way to get a hill with the ZF auto? kick it back out of drive into 3, (put it in sport mode if its the electronic version) and build up some speed then ease of just a touch to allow the TC to lockup (if it hasnt already) then gently apply the power again to keep the momentum up.

Thats the whole problem with a 4HP22 (ie not EH) though, it doesn't lock up in third unless you've spent the $900-odd on a third gear lock up mod. The only two parameters that determine lockup are road speed and shifter position.

=IF(logical_test=AND(logical1),[value_if_true],[value_if_false])

=IF(road_speed>80km/h=AND(range_selected="D"),[torque_converter_locks],[torque_converter_unlocks])