My girlfriends 06 Revup overheated and so I swapped out the thermostat and bled the cooling system. Drove it around for an hour while letting it idle at stop lights for 2-3 minutes. A/C blows cold and heat blows HOT. When I left her idling for around 15 minutes though, the temp SLOWLY crept up to the halfway point...then another 15-20 minutes and it went just a bit up over the halfway point and etc etc. I checked and both fans are on and spinning but they do not kick on high at all. Could it be my coolant temp sensor has gone bad and has caused the fans to not kick on to high?

 

Easy way to check is to read the temp sender's output on an OBDII scan tool with live-scan function for that sensor and compare it to a reading you get at the input side of the radiator using an IR thermometer. Those are two must-have items in your toolkit if you plan to do work on your car without blowing money on parts you don't need.

 

the temp sensor either works or it don't.

there is a relay for high speed. maybe it failed?