89 civic dx, 1.5L
The radiator on this vehicle was cracked, but is now repaired. I am not losing coolant as far as I can tell. Once the car has warmed up, the temp gauge will climb very quickly, peak a little over 3/4 and then drop back to normal. When idling there is no issue (again, as far as i can tell). it goes up and down in a matter of 15-20 seconds. I have been having issues that I think i've corrected, but may have caused other problems in the process.
There is some stop leak in the radiator (may be plugging it, then getting blown out, and plugging it, getting blown out, ad infinitum) also, with 165k miles the thermostat could be gone, except that it seems thermostat problems lead to the temp sensor reading cold, not hot.
if anyone can help me i would appreciate it very much.
thanks
jesse

 

I'd say it';s prob the stop leak in the radiator... The thermostat is there so that the engine can "warm up" to operating temp, then be cooled at operating temp. If ur thermostat is stuck almost closed, it could make engine run hot, but if it was stuck open it would run cooler than normal. take out thermostat and see if it still runs hot, then u will know what the prob is...

 

i'm thinking it was air in the cooling system. I started the engine from cold with the radiator cap off to flush the air out. i squeezed the upper radiator hose a few times to make sure i got it all. I've driven it maybe 20 miles since then with no problems.
I am thinking it was probably a steam bubble just because off how fast the temp went up and then shot back down, presumably when the bubble got past the temp sensor.
we shall see.....

 

Keep us posted...
Good Luck!