I've suddenly noticed a 11-15 degree (F) jump in my coolant temps, in both peak temp and crusing temps. Usually I run about 190 degrees (dipping as low as 186 on the highway at a steady 70 mph) but now I am running around 199-201 with peaks of 205 or more. I haven't made any changes to the coolant since a flush/refill about 18k miles ago, and the overflow bottle is at the correct level. This is an 02 WRX with TBE and a STI intercooler. Any idea what's up? Anyone with a digital water/coolant temp gauge want to compare temps?

 

anything hit your radiator? running any CELs?

 

No CELS, and zero leaks; I park in the exact same spot on a concrete driveway every day, and there is no sign of oil or coolant.

 

2 ideas.

1) did you try adding coolant?
2) is it starting to get any hotter outside?

im my rx7 there is such a noticeable difference in my cars temps between driving in the daytime compared to morning/evening time.

 

Sometimes running hotter cooloant temps could mean you have a potentially bad head gasket. Good luck!

 

OK, so I did a 40-minute drive today, about 60% highway. My top coolant temp was 195 and about 185-183 cruising on the highway, right back where it should be. The difference? I had the A/C on, which seems to draw the heat for its heat exchanger right out of the coolant. Ambient temps are high here (90 degrees) but typically that just effects how warm the coolant is when I start the car, not its actual peak temp. If the coolant is hotter than the ambient air temp, how would the air be heating the coolant? Our humidity and dew point is so low here that humidity isn't a factor either.

I know it isn't a gasket problem; I've already been through a full headgasket/camgasket failure with the wife's Legacy 2 years ago; that was a mess of coolant and oil on the floor and a host of other symptoms besides. I've got none of that.

I'm thinking I have an air bubble in the system or perhaps a bad thermostat. At 60k I am going to drain the coolant and refill with Subaru factory fluid and replace the thermostat and radiator cap.

 

The AC can actually make the engine run hotter since it increases the load on the engine to run the compressor. However the AC also runs the fans full-time so if it's not that hot outside the AC being on can help keep the coolant temps down.

 

Have you had the coolant changed lately. Getting all of the air out when you change either hoses or coolant is a pain on the 02 wrx. Even a mechanic friend of mine at the dealership says its a pain for them. Check your coolant level when the car is cool.