Gave my still good 2007 Focus to my son, who needed a car. 144,000 miles. Ran fine since new, all maintenance done as required. Two days after getting the car it overheated. Fans not running at any speed or with AC / defroster on. Replaced both low and high speed relays, fans began working as they should. Son test drove it and it overheated again. Pulled back into the garage and fans are running. Radiator was hot, could not remove cap until it cooled down. Fluid levels in the radiator are good. No idea where to go from here. Thermostat stuck open? Radiator partially clogged? Seems funny it would happen all at once after years of trouble free driving.
More likely stuck closed. Stuck open, it would not overheat. I’d replace the T-stat and see if that solves it… unless the coolant that spills out when you change it looks like mud… If a coolant flush hasn’t been done in a while, might be good to do it now.
13 year old car with XXX miles… stuff breaks. Usually at the oddest times.
Thanks! I figured if it was stuck closed the radiator would not get as hot as it does. If it was stuck open, maybe the coolant was going through too fast and not having time to lose heat in the radiator. Either way I’ll do a flush and check the thermostat. It was replaced about a year ago, a real pain to get to, but it’s possible it could have gone bad already.
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Aftermarket thermostat?
Yes, aftermarket from Autozone.
You can test a thermostat in a saucepan on the stove, with a thermometer…not that you want to have to dig it out again. Good luck and please keep us informed.
Turned out the new thermostat I installed 4 months ago was bad. Put a new one in and no more overheating.
That’s a myth, not possible.
I have access equipment in a university thermodynamics lab.
I did an experiment to disprove this.
Unless there’s cavitation, heat transfer rises with flow rate.
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