VW Transporter Cooling Issues Point to Faulty Thermostat

I experienced a very similar issue with my 2018 VW Tiguan with the 2.0 TSI engine last winter. As someone with some hands-on experience working on VWs, these symptoms immediately pointed to thermostat problems. The symptoms you describe, engine overheating during normal operation and slow warm-up times, match exactly what I dealt with. My temperature sensor readings were also all over the place. After monitoring the coolant temperature behavior for a few days, I took it to my regular workshop. They diagnosed a faulty map thermostat, which was causing incorrect coolant flow regulation. The thermostat wasnt responding properly to engine temperature changes, leading to those inconsistent readings you mentioned. They also performed a full cooling system check to rule out any water pump issues or coolant leaks. The total repair came to 350€, including parts and labor. Since the fix, the engine temperature has been perfectly stable, and warm-up times are back to normal. Before suggesting specific fixes, could you share: Current mileage on your Transporter? Any recent cooling system repairs? Are you noticing any coolant loss? Does the temperature fluctuation follow any specific pattern (highway vs city driving)? This information would help determine if your issue is similar to what I experienced.

Last service was just 2 weeks ago at 58478km and they reported no issues with the cooling system components. Since then, I have monitored the coolant level carefully and noticed no loss. The temperature fluctuations seem unusual and not tied to specific driving conditions. The cooling fan operation appears normal, though I hear it running more frequently than before. I appreciate the insight about the map thermostat, that does sound similar to my symptoms. The erratic temperature control is concerning, especially since the coolant system was checked so recently. I will have the thermostat housing inspected based on your experience. Would you recommend any specific tests to confirm if the thermostat is the culprit before proceeding with the replacement?

Thanks for the additional details about your Transporter. After dealing with similar issues on my Tiguan, I can say the symptoms you describe strongly align with a faulty thermostat housing. The fact that your coolant level remains stable is actually good news, as it likely rules out more serious cooling system problems. The increased cooling fan activity you noticed was also present in my case, its the systems attempt to compensate for poor temperature control. Before replacing the thermostat, here are the tests that helped confirm my diagnosis: 1. Monitor coolant temperature with an OBD scanner during a cold start. A properly functioning thermostat should show a steady rise to operating temperature. Mine showed irregular spikes. 2. Check if the upper radiator hose gets hot before the lower one during warm-up. With my faulty thermostat, both hoses warmed simultaneously, indicating improper flow control. 3. Observe the temperature gauge during constant-speed driving. A working system maintains steady readings, while mine fluctuated even under consistent conditions. The recent service actually helps narrow down the diagnosis, since other cooling system components were verified as functional. Based on the matching symptoms and similar engine architecture, the thermostat housing is likely the root cause of your engine overheating issues. The repair cost should be comparable to what I paid (350€), assuming no additional issues are found during replacement.

Thanks for the diagnostic suggestions and sharing your Tiguan experience. Those tests make sense, especially checking the radiator hose temperatures and using an OBD scanner to track the warm-up cycle. My regular mechanic can perform the thermostat housing inspection next week. Given the similar symptoms and the fact that my cooling system was recently checked, I feel more confident now that we are looking in the right direction with the thermostat. I will run those tests you mentioned before the appointment. The temperature control issues and erratic temperature sensor readings match your experience exactly. At around 350€ for the repair, it seems worthwhile to address this now before risking any cooling system damage from continued overheating. Will update once the thermostat housing inspection confirms the diagnosis and repairs are complete. The detailed information about your experience really helped narrow down the likely cause.