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Normal coolant temp, thermostats, and AC off due to high engine temp

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Late last week on the way home I suddenly got the message "AC off due to high engine temp" message, and the temp gauge starting spiking. I had just checked the coolant level the day before and it was fine, but turned the heat and fan on high and pulled over as quick as I could and checked the level. It was low. I added coolant, as then started up the Cruze, and checked the temperature. The gauge went back down so I started driving again.

I kept monitoring the temperature display, as I have the digital readout, my Cruze being a 2012. Driving temperature was now running low, in the 150 degree range and it wouldn't go any higher.

What I think happened is the thermostat got stuck closed, blew off a bunch of coolant out of the coolant reservoir, and then somehow the thermostat got stuck open. Whether this was by accident, or by design to protect the engine, I don't know.

I bought a new thermostat and replaced it over the weekend. Today, I monitored the coolant temp all day, driving about 200 miles for work, and noticed something different. Coolant level is still fine, but my normal "high" coolant temperature is now 195 to 200 degrees. If I really push it, I can get it as high as 207. Normal operating temperature used to be in the 210 to 220 degree range.

I researched the thermostat part numbers, and as far as I can tell, the part number has changed. It used to be part number 55579010, and now it is 55593034. What is going on here? As I understood it, the thermostat is electronically controlled, so why did my "normal" coolant temperature change?
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I would suggest it is more likely that the heating element of an older thermostat is deteriorating. The amount of current being passed through the circuit changes in time to achieve the same effect on system temp (either by pulse width modulation or voltage).

Similar to a slowly clogging injector, the electrical effort to maintain the status quo is slowly increased over time. Meanwhile, no other difference is engine data would be observable. Eventually the electrical effort able to be delivered maxes out. In the injector analogy, you are pulsing the injector for the whole duty cycle and it can deliver no more - if the system deteriorates any further NOW you will lean out. Back to the thermostat case, NOW you can no longer control overheating and you get the A/C shutoff business.

When you install a new thermostat unit, there are conceivable programming scenarios where the old learned duty/voltage to the heater element will be maintained until the ECU learns that it can get better fuel economy by incrementally increasing the "standard" operating temp to the hotter end of some of the figures discussed here.

*EDIT - except that less electrical effort to the heater element equals higher temp the way it has been described above...? That makes no sense from an electrical engineering perspective. I'm going to try to look into how its controlled.
 
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