I think I have a bad t-stat

[bil-loc]

My 89 coupe is running hot about 260 then red light comes on. I put on the heat and the temp drops to about 240. Is my t-stat bad? and what should be a normal temp on a 60 degree day

 

[Tuna]

The t-stat could be sticking shut but the radiator may be covered with paper, plastic, bugs, etc. causing the problem.

Turning the heater on creates a second heat transfer point and lowers the temp so the radiator isn't getting the job done. Check that first to make sure it's not obstructed before pulling the t-stat.

On a 60 degree day, I wouldn't expect much over the t-stats open value. Even 240 is too high for an 89.

 

[jeepie]

What he said. Are your fans turning on ?

 

[vader86]

Your main fan should be coming on between 225-230 on your gauges.

Your radiator is blocked with dirt, between the condensor and radiator. Remove the shroud and clean in between.

Replace the tstat with a 160 or 180.

 

[cntrhub]

If you have time in the morning, start the car and let the engine warm up. Keep feeling the upper radiator hose for heat. It will stay cold in the early part of warm-up, but when the engine block starts to act as a heat sink, the stat will eventually open and you'll feel warm/hot water start to flow and begin to heat the hose that was cold a few minutes ago. Figure your stat is working properly then. Now, you can also pull the radiator cap off before starting the car, and see if the radiator coils are clean and not gunked or clogging the passages. Was the coolant level low or up near the neck? Keep the cap off for the next test. Now start the car up (again, with the radiator cap off) and check that the water is not bubbling. You'll see that right off and know you have a head gasket problem. That bubbling is compression entering the cooling system. If everything is cool (pun intended) and no bubbles are present, then replace the cap now! Keep the enging running and then check that upper hose for heat in a few minutes. Is the fan clutch working? It should be locked and ready to go in the morning. If you sustain a 3,000 rpm rev, the engine and the fan should be running the same speed. If you see the fan is not moving and lags, then it could be your fan clutch going south. Just a few more suggestions for you to check out.