Rep Power: 0

My 93 Civic SI was always fine when it came to engine temperture, until today. The temp. gauge was going up, almost to max when I was stopped at a red light. It would continue to slowly rise until I hit about 3rd gear and the suddenly and instantly drop to half-temp. It did this for a 20km trip. Having some knowledge, I checked to make sure that the fan was coming on, checked the coolant level which was a little low so I topped that up, checked all over for coolant leaks, checked the engine for coolant in the oil, I couldn't find anything. When I left the place I went to, after 40 minutes of cooling down in cool tempertures, as soon as I fired it up the needle for the temp went straight to just below half-temp and hasn't moved since then. This leads me to beleive it's a sensor of some sort, but any input would be greatly appriciated.

Thank you in advance.

 
Rep Power: 0

well i guess i would say first just throw in a new thermostat cus its cheap. possibly coolant temp sensor going bad idk. those are cheap to