VW Sharan Overheating: Bypass Valve Under Suspicion

Having dealt with a similar issue on my VW Touran 2002 diesel, I can relate to your overheating concerns. My experience level with car repairs is moderate, mainly from working alongside mechanics during various repairs. The symptoms you describe match exactly what I experienced, engine overheating and error codes. The bypass valve was indeed the source of my problems, but it turned out this was actually caused by a previous coolant leak repair that wasnt done properly. In my case, the workshop discovered the original coolant leak had allowed air into the system, which damaged the bypass valve over time. Since the initial coolant leak repair was still under warranty, they replaced the bypass valve at no cost to restore proper fuel efficiency and prevent engine stalling. To provide more specific advice about your situation, could you share: What error codes are you seeing? Does the overheating happen more during city driving or highway speeds? Have you noticed any coolant loss or puddles under the car? Were there any recent repairs done before these symptoms started? These details would help determine if your issue follows the same pattern as mine and guide you toward the right car repair solution.

Thanks for sharing those details. My Sharan just had its service last month, so these symptoms are quite concerning. After reading your reply, I checked under the car and noticed small coolant spots, suggesting this might be connected to a coolant leak rather than just the bypass valve. In response to your questions, the main error code is P0118 (engine coolant temperature circuit high input). The overheating occurs mainly during city driving, especially in stop-and-go traffic. The temperature gauge starts climbing after about 15 minutes of driving. The power loss becomes noticeable as the engine temperature rises, which seems to match your experience with the damaged bypass valve. No recent repairs were done besides routine maintenance. Has anyone checked if your cooling system maintained proper pressure after the repair? This might help pinpoint if Im dealing with a similar underlying issue.

Thanks for those additional details. The P0118 code and symptoms you described definitely mirror what I experienced with my Touran before getting it fixed. The coolant spots you found are a crucial clue, this matches the root cause pattern of my issue exactly. After my repair, the shop performed a cooling system pressure test which revealed the system was maintaining proper pressure. They explained that failing pressure tests often indicate either a persisting leak or air pockets in the system. In my case, addressing both the coolant leak and bypass valve was necessary for a complete fix. The power loss during temperature increases is particularly telling. When my bypass valve was damaged, the engine would lose significant power once hot, especially in traffic. The combination of coolant spots, power loss, and overheating strongly suggests youre dealing with the same underlying problems I had. Given that your service was recent, its worth having them check their work. Sometimes coolant leaks can develop shortly after maintenance if any cooling system components werent properly tightened. Based on my repair experience, requesting a pressure test would be a good starting point before replacing parts.

Thanks for the detailed information. I realize now this might be more complex than just a bypass valve issue. The coolant leak spots definitely changed my perspective on the problem. Will contact the service center about these symptoms, especially since they handled the recent maintenance. Going to specifically request they perform a cooling system pressure test first, rather than jumping straight to parts replacement. Makes sense to check if theres a connection between the recent service and these new issues. The engine overheating during city driving matches the pattern you described. Will monitor the temperature gauge more closely and avoid heavy traffic routes until this gets resolved. Might also start carrying extra coolant just in case. Good to know about the potential link between the coolant leak and bypass valve damage. When I take it in, will make sure they check both issues rather than focusing on just one component. Would you mind sharing what the total repair cost was in your case? It would help set expectations for what Im looking at, especially if both the leak and bypass valve need attention.