2013 Texas Edition overheating

I have a 2013 Texas Edition, 4.6L

It has started overheating (not horribly, but enough that when I turn the car off after a drive, it overflows the overflow tank).

I changed the thermostat, and checked fluid levels. It's low, but only after blowing coolant when I stop the engine.

I've cranked it from cold, with the radiator cap off, and topped off. It never seems to suck coolant. But nothing seems to be leaking from the water pump seals. Could it still be the water pump? I thought when a water pump goes bad, it blows the diaphragm out the side of the pump.

What should I do next?

 

Check your radiator cap and thermostat. Sometimes the cap seal fails and ends up lodged in the thermostat. Or, could just be a bad thermostat that won't open.

 

I changed the thermostat yesterday morning, and refilled. Nothing changed.

 

Combustion leak test

 

So this all started the day after I had an emissions test done. For an inspection in Montgomery County Texas, they do all the regular checks, plus emissions and maybe combustion.

I have the water pump off, and it looks fine! The coolant looks great! What else could it be? The truck runs like a top, and has never overheated. Is there an electrical control somewhere? or... what in the world?

 

Harbor freight has a tester for around $32 or take it to a shop and have it done.

 

Clutch fan