96 Jimmy cooling problem

The temperature on my 96 Jimmy runs right 190 degrees in town without the air conditioner on. It seems to do ok in town with the air on. If I take it on the expressway, with the air on, the temp creeps up to around 210-212. If I turn the air off, it cools back down to 190. I have flushed the radiator, replaced the thermostat, and back flushed the heater core. The heater core was stopped up as I was not getting any hot air through it when the heater was on. Now that I have back flushed it, there is plenty of heat. i thought that was my problem. The water pump is not leaking or making any noise. Could it still be bad? Also, what about the fan clutch. It seems to be ok, though. Any help will be appreceated.

Jeff

If it is cooling good at slow speeds and idle.
Your pump and fan clutch and rad is good.
On a long steady pull or hill does the tempt go up fast or slow.
Does it ever boil over?
First try another stat and verify tempt gauge is right.
MT

The temp goes up slowly. I have replaced the thermostat with one from Advanced auto. I did not get the heavy duty one. It doesn't boil over, just stays around 210-213 degrees. As soon as I turn the air off, it comes down. I will try a GM OEM stat. Thanks for the reply.
Jeff

You are welcome.
It is normal for temp to raise some with air on.
But it should do better on the road than slow speeds or sitting at stop light.
Also make sure the tempt gauge is reading rght.
GOOD LUCK
MT

Thanks Mt-2500. I purchased the OEM thermostat and installed it. I worked. It runs normal all the time now. I will always buy OEM for thermostats. Any other parts that work better when they are OEM?

You are welcome and thanks for posting back the fix and how it went.