i drained and flushed my radiator to see if this would fix the problem, at first it seemed as though it did and the temperature remained at about the half way point of hot and cold for a good 30 minutes sitting idle. Next i decided to drive it the temperature remanied at the half way point for about five minutes but quickly after driving at abou 60-70 mph the temperature needle began to rise quickly, in about less than thirty seconds it was almost at the redline......does this sound like a thermostat problem?

No, to me it sounds like a radiator that has restricted flow. It can handle the heat of relatively slow speed drving, but not the extreme heat produced by highway driving when the engine RPM's are constantly higher. If the thermostat were sticking closed, the car would overheat even at idle within about 10 minutes. You don't give any information on the car such as the engine, the mileage and the type of maintenance the cooling system has had. That makes diagnosis very difficult. Thinking about all of the possible problems, I would still change the thermostat first, if only to eliminate it as a possible problem. It is cheap and easy to do. I would also change the radiator cap to eliminate that too as a possible problem. Again it is very cheap to do. If these two things don't solve your problem (and I doubt that they will) I would then check all the hoses for softness; they could be collasping and restricking flow. If you find nothing wrong with the hoses, I would next remove the radiator and send it out to be flow tested. If it really looks bad inside you may be better off just replacing it.

Mike

its a 90 camry 4 cyl with 250k plus, i have only had the car for about six months but i dont think that the previous owner did much maintenance on it...... yeah i replaced the termostat and the same thing happened, only this time my friggen radiator kinda cracked, there was a little leak but after driving it again the pressure in the radiator was so strong that the leaky crack went from about 1 inch to about 4 inches, i know now that i am gonna have to replace the radiator, but what is causing the pressure to get trapped in the radiator?