Driving up a hill and the gauge went all the way up and the red light came on. turned on the cabin heater at full blast and it went back down again pdq.
Reading through OBDII port and temps are sitting around 220-235F during normal driving, fans are running, quite hard at times and after stopping and removing the key. No steam or coolant escaping.

Car had new water pump and thermostat/housing/tower/temp gauge last year/15,000 miles ago. After market parts. Coolant level is good, bleed screw produces only coolant, no air.

Infra red sensor gun says top hose is around 200F and the lower one is more like 140F.

Thoughts? Is it the thermostat, the water pump, the temperature sensor?

Had the same thing a while back twice

it sorted itself out
2 years no problem since.
maybe just gremlins in sensor

Had the same thing a while back twice

it sorted itself out
2 years no problem since.
maybe just gremlins in sensor

I would bet on the sensor going bad. Your OBD temps seem too high. The sensors often go open part way through their sweep which will give a false overheat condition.

I swapped out the thermostat and it looks like the problem is cured.

We soared up the big hill near here with no concerns at all.
I guess I'll give it a few more trips out to confirm this, but seems promising for now.

Too late for me to edit the last response, so the update goes here.

New thermostat has cured the problem, I never hear the fans running at the end of a journey and the gauge remains in the middle all the time.
Driven a few hundred miles, climbed a few thousand feet up from the valley, no issues.

Congratulations on solving the problem

Best regards,

Thomas