A friend of mine said he took his 2000 outback to the shop because it started to overheat. The shop said he has transmission fluid in his radiator. If that is the case and there is a hole in the radiator wall next to the tranny cooler part of it, wouldn't there also be coolant in his tranny?

Not necessarily, but he should definitely check it.

Trans fluid is under much higher pressure, so can be forced out of a small pinhole or split in the cooler. When the engine turns off and the trans stops pumping the pressure in the radiator pushes the opposite way and can close the hole which prevents coolant pushing through.

how positive are they it's actually leaking?  that's not very common to have happen. 

 

as an illustration, picture scaled rust where it's not exactly a hole, the fluid finds and seeps through slowly and can vary quite a bit in how it does it. 

Is the coolant nasty-looking? Any signs this car has been run with straight water and no antifreeze? I'd be suspicious of an internal head gasket leak and a possible wrong diagnosis about the trans fluid. But, if there's any doubt, one test could be to disconnect the lines to the cooler and temporarily connect them together. Run the car a little and watch for; A. leakage of coolant from the coil. B. overheating

also, the thermostat MUST be OEM-style, with the larger wax capsule.

Don't run the transmission too much if you feel there's coolant mixed in the fluid!

while pricey and a little bit of a hassle, fluid samples could be sent to Polaris or Blackstone labs.

Edited August 23, 20169 yr by 1 Lucky Texan