It's 110 in the beautiful AZ sun and the car starts to overheat after driving 10-15 minutes. The overheating is very slight, in the 220-225 range. The gauge will linger just above half way when on the freeway or driving around town. It never really climbs. Radiator, main thermostat, and coolant completely replaced/flushed about 2 months ago (used to work at Firestone, got it done properly by one of the techs I trust). Coolant temp sensor has about 1.5-2 years of life on it (Beck/Arnley).
Here's what I do know:
No visible leaks at all. Spent a lot of time looking around with the car parked both in the morning and after driving for a while.
Fans come on. The cooling fan module was also replaced about 2 years ago.
With radiator cap off, can clearly see water circulating. No whirring noises or weep hole leaks from water pump.
When burping the radiator (using the cool radiator funnel tool), I don't see any oil sheen, bubbles, boiling, etc from the coolant.
Coolant in the overflow stays at a relatively consistent level.
Any ideas? The only thing I can think of that may be failing is the Water Control Valve aka second thermostat. Anyone have experience replacing one of those? Or could it be the "new" thermostat has failed?