Either thermostat or head gasket going bad.
This is a discussion on Temp Gauge Rising after DP & UP Install! within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Either thermostat or head gasket going bad....
Current Car: 2015 Honduh Civic SIgh
Previous Cars:2014 Golf TDI, 2012 WRB WRX Hatch, 2004 RSX-S, 1998 Grand Prix GTP
"Isn't it amazing how smart you feel when you just aren't being stupid?"
But if it was a head gasket issue wouldn't I be losing coolant? Or having some black scum in my overflow tank? Or having frothy oil?
I'm showing none of these symptoms....
BUT if I open my overflow tank could it be air getting into there and causing it? Because I opened it for a bit to look in....
"From a little spark may burst a mighty flame." - Dante
"The stitch is lost unless the thread is knotted." - Italian proverb
Or maybe the fan has a problem. Just a guess.
Well, I flushed the coolant. What came out looked like it was VERY old and possibly never flushed before. Looked like lemonade tea...I threw in 2 Gallons of Subaru coolant (pre-mixed) and Conditioner additive as well as changed out the thermostat and gasket...the gasket looked a bit beat but the old thermostat didn't look too bad. Car has no issues since and it's been a week since I flushed it.
So I still have no idea why it was acting so strange. But I think it either had to do with the coolant being old or bad t-stat or t-stat gasket....
My car had the same exact problem. 05 WRX. Temp would rise to 3/4 then go back down. Did it off and on for a month or so, then changed thermostat and coolant. It was fine for a week or so then went downhill and got progressively worse... Leaking headgasket on #2 cylinder. I will also note that the problem started directly after flashing a stage 1 tune... The added pressure undoubtedly caused the problem.
Also the radiator cap not holding the right amount of pressure could cause the overheating problem.. Just something else to look at if it continues in the future.