[TurboBimmer]

Here are my latest experiences:

Last weekend, I've driven two 335i's on a trackday in hot summer heat (85°F):

- my own 6AT car equipped with ER Sports OC, AR Design OC in front of the radiator and PPK radiator.

- a friend's 6MT car with upgraded OC.

Same tune, similar suspension mods, same day, same track.

I managed to overheat my car within two hard laps, water temps going above 240° and power completely cut by the ECU.

In the 6MT the car could be pushed no problem for a 30 minutes session.

So this made it clear for me that the real culprit is the heat exchanger in the radiator: the 3 lowest rows are used by the transmission oil which exchanges the heat with the engine coolant. This is fine when the engine is cold as it helps to get coolant temps up quicker, but on the track it becomes a handicap where the hot tranny oil simply heats up the coolant even more.

What we need is an external tranny cooler to keep both circuits separated.