Impreza overheating light coming on

[walkerjc]

I have a 2010 Subaru Impreza 2.5i non turbo that i bought about a year ago. The guy who had it before me redid the head gaskets and some general maintenance. I have put maybe 1000 miles on it and it now has a p0137 code (which isnt really a concern to me, just thought to mention it for context?) and the overheating light came on flashing and then solid after driving for about 20 minutes. I pulled over and let it idle until the light went away and kept driving for about 30 minutes slower, with no light. When i drove it again, the light came on same as before and i stopped and it went away, just like before. I had the heat inside the car on max, btw, it was around 25 degrees fahrenheit. I got out and looked at the cooling fans and they were both running smoothly and well, so they arent the problem. I thought it could be a thermostat or maybe a bubble in the coolant system somewhere? I do realize it could be the head gaskets even though they were changed in the last 2000 miles but i think it is unlikely.

so to sum up:

problems:
p0137 code (not really concerned abt more for context)
overheating light came on after about 20 minutes of driving

recent maintenance:
oil change about 1000 miles ago
head gaskets within 2000 miles ago
spark plug wires within 2000 miles ago

misc. info:
abt. 182k miles
manual transmission
completely stock besides wheels

Im really only concerned about the overheating light and would appreciate any amount of knowledge and information regarding possible problems and fixes, thanks in advance. I will be testing for a few thing and will update on that later.