CT6 Hybrid Thermostat Causes Wild Temp Swings

Had similar temperature control issues with my 2015 CT4 Hybrid at 130000km. The cooling system would fluctuate unpredictably, sometimes overheating, other times staying cold for too long. The temperature sensor readings were all over the place. The root cause turned out to be a defective map thermostat, which was failing to regulate coolant flow properly. The thermostat would stick in unusual positions, causing these erratic temperature swings. This is a known weak point in the cooling system of these models. The repair involved replacing both the thermostat and temperature sensor as a complete unit. While not a major repair in terms of complexity, leaving it unfixed can lead to serious engine damage from constant temperature fluctuations. Key symptoms that matched your situation: Inconsistent warm-up times, Unusual overheating episodes, Temperature gauge showing irregular readings, Issues appearing gradually over time Would strongly suggest having the cooling fan operation checked as well while diagnosing the thermostat, as they work together to maintain proper engine temperature.

Had exactly the same cooling system troubles you described. My mechanic confirmed it was indeed the thermostat causing those temperature swings. The repair fixed it completely and my Cadillac has been running at proper temperature since. Do you recall the total cost for your thermostat replacement? In my case, they also recommended flushing the entire coolant system and checking the water pump while they had it open. Wondering if you needed any additional repairs after getting it fixed or if the thermostat alone solved all the temperature issues.

After replacing the defective map thermostat in my CT4, the engine temperature stabilized completely. The total repair came to 350€, which included labor and parts. The cooling circuit motor was also found to be defective during inspection, so they replaced that as well while the system was open. Unlike your case, I didnt need a full coolant system flush or water pump check. The thermostat housing replacement and cooling circuit fix were sufficient to resolve all the temperature fluctuations. Its been running perfectly for about 40000km now with no overheating issues or irregular temperature readings. The engine now warms up consistently and maintains proper operating temperature, even during long drives. This repair proved to be the complete solution, no additional cooling system work has been needed since. If your mechanic is suggesting a full system flush and water pump inspection, its good preventive maintenance, but in my experience the thermostat replacement alone should resolve the main temperature control problems.

After my recent visit to the mechanic, I can confirm the thermostat was the main culprit causing my temperature control issues. The total repair ended up costing 450€, which included the thermostat replacement, coolant system flush, and a thorough inspection of the water pump. The mechanic found some minor corrosion in the thermostat housing, but thankfully the water pump was still in good condition. They completed the work in about 4 hours, and the engine overheating problems disappeared immediately. The car now warms up normally and maintains consistent temperature. For anyone facing similar symptoms, definitely get the thermostat checked first before assuming more expensive repairs are needed. Getting the coolant system flushed while they had it open was worth the extra cost for preventive maintenance. Three months later and the temperature gauge stays steady, no more fluctuations or warning lights.