Q7 Bypass Valve Failure Leads to Engine Overheating

I had a very similar issue with a 2019 Q8, and it turned out the bypass valve wasnt actually the root cause. After engine stalling and overheating issues, I discovered it was related to a poorly done coolant flush from a previous service. Having some experience with these engines, I noticed the symptoms match yours exactly, error codes and overheating warnings. The workshop found that debris from an incorrect coolant mix had caused a minor coolant leak, which then affected the bypass valve operation. The fix was actually covered under warranty since it was a consequential issue from the previous service. They simply cleaned the system, replaced the coolant with the correct specification, and reset the engine management system. No parts needed replacement. Before jumping to conclusions about the bypass valve, could you share: When was your last coolant service? What error codes are you getting specifically? Does the overheating happen more during city driving or highway speeds? Have you noticed any coolant loss or puddles under the car? This information would help determine if youre dealing with a similar situation or if its actually a bypass valve problem.

Thanks for the reply and questions. My vehicle has 88038 KM and the last major service was completed 3 months ago where they did check the vacuum system and cooling components. The engine stalling occurs mainly during city driving, with the engine temperature rising quickly after stops. No visible coolant leaks under the car, but I have noticed the coolant level dropping slightly between checks. The error codes are P2181 and P0597, which point toward cooling system issues. The previous service included a coolant system pressure test, but they didnt perform a full flush. Given your experience, I will have them check for debris in the system before replacing any parts. This could explain both the fuel efficiency drop and the intermittent overheating issues I am experiencing.

Thanks for providing those details. Having gone through this exact situation with my Q8, the symptoms youre describing sound eerily familiar, especially the engine stalling during city driving and gradual coolant loss. The error codes P2181 and P0597 typically indicate cooling system problems, but they dont automatically mean a bypass valve failure. In my case, these same codes appeared because debris was restricting proper coolant flow, causing the engine overheating and system pressure irregularities. Since your last service checked the vacuum system but didnt include a coolant flush, I strongly suspect youre facing the same issue I had. The power loss and engine stalling during city driving are classic signs of coolant flow restrictions, rather than a bypass valve malfunction. Here is what worked for me: Full cooling system flush with proper pressure cleaning, Thermostat inspection, Coolant replacement with factory-specified fluid, System pressure test after service The dropping coolant level between checks, combined with no visible leaks, suggests the system might be operating under incorrect pressure, just like in my case. Id recommend getting these checks done before authorizing any bypass valve replacement. Would you mind checking if there have been any changes in engine temperature behavior during different weather conditions? This could help confirm if were dealing with the same root cause.

I really appreciate the detailed response and shared experience. After reading your feedback and the suggested steps, Im feeling more confident about the diagnosis. The engine temperature actually does vary more noticeably during warmer weather, which seems to support your theory about restricted coolant flow rather than a bypass valve issue. The quoted repair cost for a complete bypass valve replacement was 850 Euro, so exploring the cooling system flush first makes much more sense. The car repair shop initially pushed for the valve replacement, but your experience with similar engine stalling and air intake system symptoms has given me a better direction. I will schedule the cooling system flush and diagnostics you suggested. The power loss during city driving matches exactly what you described, and checking the thermostat before replacing major components is definitely the smarter approach. I expect the engine overheating warnings should resolve once the cooling system is properly flushed and the correct coolant is installed. Will update once I have the service completed. At least I know Im not looking at a major repair if the issue is just debris affecting the coolant flow.