I have a 2009 Aveo5, base model, no A/C. ~260,000 miles.
It is running warmer than usual, with the heat gauge just shy of the halfway mark; it normally sits just over the 1/4 mark. In addition the engine bay gives off a considerable amount of heat after driving. Here is a description of what led up to the problem and what I have done since....
A few weeks ago I was replacing the blower motor (GM 95978693) and cabin air filter because I wasn't getting any air movement from the vents. I noticed the lower radiator hose and one of the heater core hoses were starting to balloon, so I replaced them too. I also decided to flush the radiator (with distilled water) and add new coolant (DexCool). I followed the flushing procedures in the Haynes manual.
After replacing the hoses and flushing, I noticed a leak and found several cracks in the coolant expansion tank. At this point, I decided to replace the expansion tank along with the rest of the cooling system hoses.
After replacing the expansion tank and hoses and refilling the coolant, I noticed the radiator fan was not turning on after reaching operating temperature. This is the first time I noticed the temperature raising higher than normal.
I replaced the Fan Hi Relay (GM 6484304), the Fan Low Relay (GM 96590287), and the Radiator Fan Resistor (GM 94812213). The radiator fan still did not work, so I replaced the whole radiator fan assembly.
The radiator fan now works properly, but the temperature gauge still indicates the car is running hotter than normal.
I am wondering what could be causing this problem. Thermostat, water pump, something else? The water pump was replaced ~20,000 miles (6 months) ago.