2005 TL 6MT, ~220,000 miles.

Today my CEL came on, ScanGauge reported code P0128. I open the hood and the coolant expansion tank is over the "max" line, and it looks like some coolant has spit up around the engine bay, but the system does not appear to be leaking.

The car sat for about an hour after being driven and the ScanGauge showed a normal coolant temp (about 150 degrees while idling after I'd just turned the key) but the air intake temperature seemed really high at 125 degrees.

Google says the codes means "Coolant Temperature Below Thermostat Regulating Temperature" and possible culprits include faulty t-stat or air intake temperature sensor... because of the high reading I'm thinking the latter.

But any other ideas are appreciated. Perhaps I need to swap the t-stat too? Also, should I try and drain the expansion tank to below the "max" line?

 

Resolved.

So, it turned out that the straw extending into the coolant expansion tank was... missing? Not sure how that happened or why it suddenly became a problem. but basically, the car was unable to put its coolant back into the radiator after it went into the expansion tank. Odd. But at least it was an easy fix.