Ron (Houston):
ADias:

 What is this center radiator for? Engine coolant? Engine oil? or Transmission oil?

I remember in 996 Tips they all had middle transmission oil coolant.

Not strictly correct, but the effect intended was the same.
The center radiator cooled the "engine" coolant just as the two standard side radiators did, but the 3rd. radiator was added to Tip cars because these transmissions shed more heat than manuals, leading to the Tip boxes being equipped with oil-to-water heat exchangers which passed the tranny's surplus heat on to the water coolant, which was then conducted to all three radiators at the front of the car.


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fritz