I agree with you. Chances are the radiator isn't the problem, so a flush would most likely be a waste of money.
As far as the head gasket question, you would need to do a compression test. Then you could check to see if there is a cylender with low compression.
If this only happens with the ac on and you have done everything you described, I question if there is a problem at all other than a faulty coolant temp sensor or some short that is causing the gauge to raise. Another thing you could try (to make sure the gauge is accurate) is to rent a radiator thermometer. With the engine cold, open the radiator cap, put in the thermometer, start the engine with the AC on and see what temp the coolant in the radiator gets. It should stay around 200 degrees F.
Here is a how to for checking compression if you need it:
Something tells me with everything you have done, something is causing the gauge to misread.
Let me know what you find.
Thursday, July 16th, 2009 AT 10:00 PM