Passat Hybrid's Conflicting Temperature Troubles Revealed

Had the exact same symptoms on my 2019 VW Arteon Hybrid. The temperature sensor readings were erratic, showing both overheating and slow warm-up issues. The root cause was indeed a defective map thermostat in the thermostat housing assembly. These electronic thermostats can fail in a way that disrupts proper temperature control, causing the system to either stick open or closed. The repair involved replacing the complete thermostat housing unit since the map thermostat is integrated. While the water pump was exposed during the repair, the mechanic confirmed it was working properly. The engine overheating issues were resolved immediately after the replacement. It was a significant repair that required specialized diagnostic equipment to confirm the faulty thermostat readings. The job took about 4 hours since accessing the thermostat housing on these hybrids requires removing several components first. Would strongly recommend getting this checked soon, as continuous overheating can lead to more severe engine damage. Make sure to find a shop with hybrid powertrain experience, as the cooling system on these models is more complex than conventional engines.

Thanks for sharing your experience. Really helpful since I was also suspecting the thermostat housing was the culprit in my coolant system issues. Quick question, would you mind sharing how much the complete repair ended up costing? Also curious if youve had any temperature control problems since getting it fixed? Just took mine in yesterday and waiting on the final diagnosis from the shop. Hoping its just the thermostat and not more extensive engine overheating damage.

Since getting the thermostat cooling circuit motor replaced two months ago, the temperature control system has been working flawlessly. The repair cost came to 350€, which included the new map thermostat, labor, and a complete cooling system inspection. The mechanic confirmed what I suspected, the thermostat housing was malfunctioning, causing those erratic temperature readings. They ran a full diagnostic check after the repair to ensure the temperature sensor was responding correctly and the water pump was circulating properly. For peace of mind, the shop also pressure-tested the entire cooling system to rule out any other issues. The engine now warms up normally and maintains steady operating temperature, even during long drives. No more overheating warnings or cold-start problems. Based on the symptoms you described, sounds exactly like what I experienced. If caught early enough, a faulty thermostat usually doesnt cause additional engine damage.

Just got back from the shop and wanted to update everyone. After checking everything out, they confirmed it was indeed the thermostat housing causing all my temperature control problems. The repair ended up costing 380€ including parts and labor. The mechanic showed me the old thermostat, it was definitely stuck, causing those weird temperature fluctuations. They did a thorough check of the water pump and coolant system while they were at it, which thankfully showed no additional issues or coolant leaks. Car has been running perfectly for the past week. Engine warms up normally now and maintains steady temperature during my commute. No more overheating warnings. Really glad I got it sorted before any serious engine damage occurred. Appreciate all the advice here, helped me feel more confident about the diagnosis and what to expect from the repair.