[john70t]

WAG here:
-Oil into the coolant would indicate that side had the most positive pressure.
The PVC or something else in the EVAP could stick shut, and then blow-by could pump the engine case up like a balloon. There are radiator pressure testers that find leaks.

-Scott may be on to something. The oil/coolant mechanism might be blocked. An infrared thermometer on the hoses before and after will indicate if there is flow.


Besides an intermittent FP relay and leaking sunroof and electrical problems, my '89 Golf also had an overheating problem:
-Jumpered the fan direct and it was good. Tried three different thermostats. They are located under the pump so bleeding was a problem. New thermo fan switch. New radiator. Tried bleeding it six different ways to sunday (squeezing the hoses while parked on steep hills, filling up each side separately, etc). I was still probably doing it wrong.

-Never did fix it. It was probably a blocked exhaust or an ECU preventing the fan running in retrospect. Something else. Timing was right. Had normal power when cool.

-I drove around with the A/C on high. The extra fan pulls more air through the radiator. Or full heat with all the windows down. Pulled over when it got to max. It lasted a few years that way. Terrible way to drive though.

-The heater core finally exploded inside the car right before the Bay Bridge. Air bubble or rusted out. I walked to a hardware store and looped those hoses back into the engine.
Interior heat is tangential to engine cooling.