VW Taos Thermostat Issues Causing Temperature Swings

Had the exact same symptoms on my 2021 VW Tiguan last winter. After some basic experience working on cars, I could tell something was wrong with the temperature control system but needed professional help for a proper diagnosis. The workshop confirmed a faulty map thermostat was causing irregular coolant flow through the system. They performed a pressure test on the coolant system to rule out any leaks, then used diagnostic equipment to monitor the thermostat behavior. The symptoms match yours exactly, slow warm-up when cold but overheating during regular driving. The repair cost me 350€ including parts and labor. Since the fix, the engine temperature has stayed perfectly stable. The new thermostat maintains proper coolant flow and temperature control. What engine variant does your Taos have? This would help determine if the thermostat setup is similar to what I dealt with. Also, have you noticed any coolant loss or sweet smell that might indicate a coolant leak? These details would help confirm if you are facing the same issue. Would definitely recommend getting it checked soon, as ongoing temperature control problems can lead to more serious engine damage if left unaddressed.

Latest service was at 140000km The intermittent engine overheating continues after checking all the basics like coolant level and visible leaks. Its the 1.5L TSI engine. No coolant loss or sweet smell detected. The cooling fan seems to work normally but the temperature fluctuations persist. The temperature sensor readings on the dash are erratic, sometimes showing normal temps but then climbing quickly during highway driving. Have not noticed any warning lights yet but the unstable readings are concerning. What diagnostic code did your shop pull to confirm the thermostat housing issue? Would help to know what to expect at my upcoming service appointment.

Thanks for those additional details about your Taos. I had the same 1.5 TSI engine in my Tiguan when I experienced similar symptoms. The diagnostic code my shop pulled was P0128 (coolant thermostat malfunction), which specifically indicated the thermostat was staying open too long. The erratic temperature readings you describe match exactly what I experienced, normal readings suddenly spiking during steady highway speeds. The cooling fan operation can appear normal even with a faulty thermostat since its running based on the temperature sensor inputs. In my case, the thermostat was actually sticking intermittently, causing the engine overheating episodes despite the cooling system otherwise working properly. At 140000km, its not unusual for thermostats to start failing. The repair solved all my temperature control issues. Make sure your shop does a full cooling system pressure test and electronic diagnostic scan rather than just a visual inspection. The total diagnosis and repair took about 4 hours at my shop. They also recommended flushing the entire cooling system while everything was apart, which helped ensure optimal performance of the new thermostat. Let us know what they find at your service appointment. The symptoms really do sound identical to what I experienced.

Thanks for sharing those repair details. After comparing the symptoms, I am increasingly convinced my Taos has the same thermostat housing issue you encountered. Your mention of code P0128 will be helpful when discussing this with my mechanic. The engine overheating pattern matches exactly what you described, normal temperature readings that spike unexpectedly during steady highway driving. My coolant system appears sealed with no visible leaks, yet the temperature control remains inconsistent. Will schedule that service appointment for next week. Planning to request both the cooling system pressure test and diagnostic scan to properly identify if the thermostat is failing. Good tip about considering a complete system flush while they have things apart. Really appreciate you confirming the repair resolved your temperature control problems completely. Gives me confidence that replacing the thermostat should fix these concerning temperature fluctuations before any serious engine damage occurs. Will update the forum once I get the official diagnosis and repair completed. The detailed experience you shared helps set clear expectations for both the diagnostic process and likely repair costs.