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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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Here's my theory and thoughts.

The wire on the thermostat is actually a heat resistor, which is commanded on to heat the coolant locally near the traditional wax pellet thermostat keeping it open.

Since the computer sensed high temperature, it commanded this resistor to produce a lot of heat, to keep the old thermostat open. So much so maybe the old thermostat mechanically failed.

The control system of the car is going to gradually reduce power to this auxiliary heater causing temperature to rise. I bet it takes a few drive cycles.

Keep your eye on the coolant level, as you may have a few air pockets in the system. Although many have said the flow from the small black line attached to the coolant reservoir is a fairly high flow. With this point being the highest in the engine I'd assume air would bleed fairly well in this setup.

I think your fine. I have the coolant display on my 2012 as well.

If I crank up the heat really fast I can see the car commanding high engine tempertures to compensate for the heater. What's interesting is when you shut the heater off. The car reaches 225-227F on the high side, thermostat opens and in this case the engine cools all the way down to 205-207F.

There was one person on the forum, the member that had the salvaged title and wrote the water pump How To. I think he may have "blown the thermostat" to pieces, and pieces mechanically got stuck in the water pump. In his case the temperatures were always high, as he had a restriction of flow.

If the old thermostat still had it's inner guts, you know you got everything, which I believe you did, since you have cold temps.

There is a bleeder on the radiator near the top on the passenger side, if I recall from reading correctly. It could be air, around the thermostat or thermostat resistor, but I kind doubt it.

While I haven't had the Cruze coolant system open, I have had a lot of air bleeding problems with GM's early models with only the coolant bottle on the firewall. The Oldsmobile Intrigue was such a problem I purchased a vaccum coolant fill tool from Amazon. I gave up with the small coolant bleed on the top of the radiator. it seemed it always had air.
 
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