VW Tiguan Erratic Engine Temp Points to Thermostat Issue

Had the exact same symptoms on my 2019 VW Golf GTI. The thermostat housing was malfunctioning, causing inconsistent coolant flow and erratic temperature readings. The map thermostat controls coolant circulation based on engine load, and when it fails, the cooling system becomes unpredictable. The repair involved replacing the complete thermostat housing unit. Main symptoms matched yours perfectly, unusual engine overheating episodes followed by periods where the engine would barely reach operating temperature. This caused the coolant system to work inefficiently. This is a known issue requiring prompt attention. Continued driving risks serious engine damage if the cooling system fails to regulate temperature properly. The repair is straightforward but needs specialized diagnostic equipment to properly calibrate the new thermostat. After replacement, all temperature regulation returned to normal. The coolant leak that developed around the housing was also resolved. Would recommend getting it checked soon, as running with a defective thermostat can lead to more extensive engine problems. Make sure they check for any damage to surrounding components while doing the repair. Some mechanics miss checking the auxiliary water pump and adjacent hoses, which can also be affected.

Thanks for sharing your experience with the thermostat housing issue. That definitely sounds like what I am dealing with on my Tiguan. The unusual engine overheating followed by cold running perfectly matches my symptoms. Do you remember roughly what the repair cost was? Also curious if youve had any other cooling system problems since getting it fixed? Thinking I should get mine looked at soon before the coolant leak gets worse or causes additional engine damage. Just want to know what Im getting into cost-wise.

Following my earlier post about the thermostat issues on my Golf GTI, got it fixed last month and the cooling system now works perfectly. The mechanic confirmed it was indeed a defective map thermostat causing the erratic temperature behavior. The total repair came to 350€, which included replacing the complete thermostat housing unit and recalibrating the cooling circuit motor. Since the fix, the engine temperature has stayed completely stable with no more overheating episodes or cold running issues. The coolant leak is also completely resolved. The cooling fan now operates normally and the temperature sensor readings remain consistent. No other cooling system problems have occurred since the repair. Really recommend getting yours checked soon, leaving a faulty thermostat unfixed can lead to more serious engine issues. The cost is worth it compared to potential engine damage from continued overheating. The diagnostic equipment confirmed the thermostat was the root cause, which matches the common pattern with these units. Once replaced, the entire cooling system returned to proper function.

Thanks for the advice. I finally got my Tiguan fixed at a different repair shop and wanted to share how it went. The shop confirmed it was the thermostat housing causing the temperature control issues. Total repair cost was 420€ which covered the new thermostat unit, labor, and a thorough check of the entire coolant system. They also found and fixed a small coolant leak near one of the hoses. The engine temperature now stays perfectly stable, no more unusual overheating or cold running problems. The temperature sensor readings are consistent and the cooling fan cycles normally. Really glad I got it taken care of before any serious engine damage occurred. The new shop did great work and took time to explain everything. Much better experience than my previous mechanic visits.