I have been having cooling issues with my sunfire its a 1998 with the 2200, I have had the same persistent issue for the past 6 months. It seems like my issue comes back to the thermostat every time. The issue started about 6 months ago, it would run fine and stay cool in town but if I take it on the highway it would run hot and over heat. So I put a new thermostat in it and it quit that for about a week and ran fine then it started running hot on the highway again so i flushed the coo;ling system with prestone cooling system flush and after it was all flushed I put new dexcool in and put a gutted thermostat in it and ran it til the end of summer and never had a problem but now its getting cold again so I need heat. so two weeks ago i bought a new thermostat and installed it it ran right in the middle of the temp gauge like it should, It ran fine for about a week until I was taking a friend home and it was a long drive just to get to the highway so I was driving enthusiastically down some gravel roads to get on the highway the we get on the highway and make it one exit down before we have to pull of because its running hot, it was 36 degrees out so I wasn't expecting it to be running hot. After it cooled of I drove 65 and it ran cool for the rest of the 20 mile drive and did fine on the 20 mile return trip. Now every time I drive on the highway (I have a 40 mile round trip to work every day) I cannot drive more than 65 without watching the temp gauge quickly rise to levels that are too high for my liking.
Sorry for the long post i just wanted to get all the info in that I could.
You sure you don't have a head gasket leaking a little?
Another thought. Are you sure it running hot? Was it boiling? If not, it may be the temperature sensor.
Pretty sure the head gasket is fine haven't seen any coolant in the oil or oil in the coolant and the coolant level never goes down. I'll have to check the temp sensor.
Yeah... I'm with Butch. Are you sure it's really running hot? Engine coolant temperature (ECT) sensors are cheap and easy to replace by yourself.
I'd try a temp sensor. They're cheap and easy. I'd also rent a pressure tester from an auto parts store to confirm that you don't have any leaks, especially at the head gasket. These motors are known to blow head gaskets fast when they get hot. They're also known to develop small cracks in the head under the same conditions. It could be that you have a small crack that only presents itself when well warmed up.
These systems are pretty hard to bleed all the air out of right away. Keep checking your level to make sure air bubbles aren't still coming out and dropping the level. Use the little bleeder screw on the hard pipe near the thermostat housing when filling. Leave it open until it is a constant stream of coolant coming out. Be careful when tightening, they twist off easy.
If you flush the coolant again, go with the green ethylene glycol stuff. It's so much better for iron block motors. I ran that in my 2200 and it seemed to work very well.
"In Oldskool we trust"
After about 5 miles on the interstate that's where the temp stays. It has a new temp sensor and a new water pump, so I'm gonna grab an exhaust gas tester for the cooling system. I tried to attach a picture.
I'll work on posting a pick later.
It's fixed, it only took two days of bleeding air out of the system but it's fixed.
Glad to hear it was so simple, even though finding the issue was so simple.
Yep. Getting the air out of those motors isn't fun. Glad you got it fixed.
"In Oldskool we trust"