Going crazy, same problems heelp!!
I have exactly the same symptoms as gskinlow experienced. I searched the posts and forum thoroughly and still need some advice.
Prior to maintenance, I had coolant light coming on intermittently in cold weather. I replaced the leaking thermostat housing with aluminum aftermarket one(ebay-deutscheparts) and the water pump. After replacing those, I replaced the oil pan gasket which I wanted to do for a very long time because it was leaking.
The oil pan gasket is now tight and I checked for leaks several times, no oil leak. I put 6.1 qt. of Valvoline Synpower 5w-30. I checked the oil level on the dipstick, its between the notches, close to the top notch (although 0.8 qt. lower) (Cleaned with a towel and inserted second time to read the oil level when engine is cold). The new thermostat housing leaked from the bottom left, so I put some black silicone, tighten the bolts and let it cure for an hour before filling. No coolant leaks from the thermostat housing now.
The overheating problem occurred after replacing those. First, I bled the system a couple of times after a partial refill. However, the car still overheated after driving 20 mins. I tried it with a/c on and off, after 20 mins it starts to overheat. After reading mkodama's instructions and many other posts, I completely drained the system and refilled it, bled it properly by doing cold and hot bleed. I changed the mechanical fan clutch and made sure the fan blades are facing the correct direction. Thermostat seems to be working because lower radiator hose becomes hot after 20 mins, but in the beginning it stays cool. Still overheating after driving for 20 mins.
I checked the voltage on auxiliary fan connector, it's 11.66v with the ignition on, 5v for the temperature sensor cable on the lower radiator hose and the resistance for the sensor is 2400 ohms (its said to be between 2-3K ohms?). I could not read the frequency on the green/black wire (it's said to be between 10 and 100Hz, pwm square-wave) on the aux fan connector.
The auxiliary fan is on when a/c runs however I am not sure it works intermittently or not(I read several posts about it). I took the electrical tape off and examined the cables(red,brown,black/green) close to aux fan connector, no rips or disconnection. The expansion tank cap is old and I think I always over-tighten it to stop leaks from the cap. I am gonna replace it today however, it was not an issue before (I read it may trigger the coolant light due to pressure).
The engine overheated on the red line for a min or so after 20 mins of driving on the highway when I tested it for the first time but no oil in the coolant. I don't think it's the head-gasket however I still cannot find the culprit.
gskinlow, you must have fixed your issue by now. What was it?
Any input will be appreciated.