VW Atlas Overheating + Power Loss: Bypass Valve Issue

As someone with moderate experience working on VWs, I had a very similar issue with my 2016 VW Tiguan. The symptoms you describe match exactly what I experienced, overheating, reduced engine power, and check engine light. The root cause in my case was actually a faulty thermostat housing that created issues with the cooling system, which then affected the vacuum system during acceleration. What appeared as a bypass valve problem was actually a consequential error from the thermostat malfunction. I got it fixed under warranty since the thermostat housing failure was a known issue. Total cost was 0€ as it was covered completely. The repair resolved both the overheating and the power loss issues. To help diagnose your specific case, could you share: Current mileage, Exact error codes from the scan, Does the overheating happen more during city driving or highway speeds, Any unusual noises from the engine bay, Have you noticed any coolant leaks or low coolant levels The air intake and entire vacuum system should be inspected as the power loss during acceleration often points to vacuum-related issues. But based on my experience, I would recommend checking the thermostat housing first to improve fuel efficiency and prevent engine stalling. Let me know these details and I can provide more specific guidance for your Atlas.

Latest service was done at 105520km, about two weeks ago. I provided the exact error codes during the forum chat yesterday, but P0597 and P0118 are the main ones showing up. The engine overheating happens mostly during city driving after the engine warms up, usually within 15-20 minutes. No unusual noises, but I did notice small coolant leaks near the thermostat housing area. The strange part is that the dealership checked the thermostat during the last service but didnt find any issues. With engine stalling and power loss becoming more frequent, Im considering taking it to a different shop for a second opinion on the exhaust system and vacuum components. Important to note that the coolant leak seems to be getting worse, especially after longer drives. Could this indicate a more serious issue with the cooling system?

Thanks for providing those additional details. Having dealt with the same issue on my Tiguan, those error codes (P0597 and P0118) strongly suggest a thermostat control circuit problem combined with engine coolant temperature sensor issues, exactly what I experienced before my repair. The coolant leak near the thermostat housing is a major red flag, especially since its getting worse. Even though the dealership didnt spot issues during service, the combination of symptoms matches classic thermostat housing failure: Coolant leaks getting worse, Overheating during city driving, Power loss and stalling, Location of the leak The bypass valve concerns are valid, but the evidence points to the thermostat housing as the primary culprit. The power loss youre experiencing is likely a protective measure from the ECU responding to the overheating, rather than a vacuum system problem. Given my experience, I recommend: Get that second opinion ASAP, focusing on the thermostat housing, Monitor coolant levels daily, Keep an eye on the temperature gauge during short trips, Consider getting the air intake system checked while its in the shop The repair cost at an independent shop was around 450€ for parts and labor when I had similar issues out of warranty. The fuel efficiency and power should return to normal once fixed. The deteriorating coolant leak definitely requires immediate attention to prevent more serious engine damage.

Based on your reply, I need to get this checked immediately. The worsening coolant leak really concerns me, especially since the engine overheating keeps getting worse during my daily commute. Ill schedule an appointment with another shop this week for that second opinion. The cost estimate of 450€ seems reasonable compared to what I was initially worried about. At least its not the complete cooling system that needs replacement. Makes sense that the ECU is limiting power to protect the engine when overheating occurs. While I wait for the appointment, Ill definitely monitor the coolant levels daily as suggested. Really hoping its just the thermostat housing causing these issues and not something more serious affecting the engine. The fuel efficiency has definitely taken a hit lately, so getting this fixed should help with that too. Thanks for sharing your experience with the similar Tiguan issue. Having the error codes matched up with your previous problem helps confirm what Im dealing with. Will update the forum once I get the proper diagnosis and repair completed.