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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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Discussion Starter · #2 ·
No one, huh?

Ok, chew on this...

Why did the thermostat part number change? I haven't heard of any specific issues with thermostats on the 1.4L Cruze. Why would they lower the normal operating temperature of the thermostat? There must be something different about it, resistance-wise or electronically. Is there a microchip on the sensor in the thermostat?

Perhaps they decided the higher operating temperature was causing an issue, either with the longevity of plastic parts like the water outlet, or that the higher temperature was causing coolant boil off and/or odor.

Or am I just blowing smoke, and there is something else going on?
 

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I am not sure that the temperature your car is running at is a problem. My daughter has a 2015 1.6T and it runs at 105C (221F) MY CTD runs at 84C (183F). It is still fairly hot here but the outside temperature does not seem to affect engine temperature much. Maybe the thermostat is at the cooler end of the normal tolerance allowed in manufacture.
 

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Perhaps they decided the higher operating temperature was causing an issue, either with the longevity of plastic parts like the water outlet, or that the higher temperature was causing coolant boil off and/or odor.

When cruising at a steady rate my 2012 runs 217-223F, always has. Floor the gas or max out the load on a hill and the temperature drops to 190-210F range.
 

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Discussion Starter · #5 ·
When cruising at a steady rate my 2012 runs 217-223F, always has. Floor the gas or max out the load on a hill and the temperature drops to 190-210F range.
That's what mine used to do. Now my normal cruising temp is 190 to 200 degrees.
 

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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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This happened to me last night! I was just driving alaong with the AC on and all of a sudden i het a message that says "engine overheating, turning off AC" or aomething like that. So i pulled over and the coolant was all over the place. So i put more in the reservoir and turned the car back on and it was like nothing happened. Did a new thermostat fix the problem? If so I'm just gonna do that myself and skip the dealer.

Sent from my SAMSUNG-SM-G920A using Tapatalk
 

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I've only had my 2013 Cruze for about two months. Operating temperatures have ranged from 207 to 223 deg. F according to my Ultragauge if that's any help.
 

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Two things come to mind - thermostat failures are uncommon on the 1.4T engine but they occur on the 1.8 engine. I wonder if you have the 1.8 engine's thermostat. The other thing that comes to mind is that GM may have reduced the operating temperature to reduce the pressure on the cooling system.
 

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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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I have that fault both in the overtemp and undertemp message...took out my temp sensor in both instances and temp between limits it should be....traced problem to sensor on drivers side of engine....connector having bad connectio.....cleaned connector and problem disappeared...code came up PO128 i believe
 
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