I first notice when it didn’t blow hot air from the vents on the drive to the gas station to fill up & the fans were blowing, but it was cool air from the radiator... (2005 Chevy Equinox 179K)
Radiator hoses were cool to touch. Got gas went the hour to work, 65-75mph, then parked looking for my turnstile gate pass, noticed the temp climbing.
Turned off, got badge, work all day, go to lunch go back, go home, no problem. Get off highway to pick up some stuff at store & beer. Sitting at the light for less than 2 minutes it almost over heats, light turns green, by the time I make the turn, go around the lot, park it, it cools down. As I’m sitting there idling the temp starts to creep up, I shut it down go get stuffs, stop for beer on way home, park it until a few minutes ago.
Bought more coolant on the way home as overflow was low. Mix that, pour in 1/2 gallon. Start car, get to temp, coolant is bubbling, cap that off, then it creeps up again, cool air from behind radiator, warm radiator hoses.
When I rev the motor as it is hot it starts to cool down, so I’m thinking either water pump is going out, or thermostat is sticking closed. I replaced t-stat not over 2 years ago.