Bora Engine Overheating Points to Faulty Bypass Valve

Had a similar situation with my 2005 Golf with the 2.0L gasoline engine. The bypass valve failure was actually a secondary issue stemming from a vacuum system malfunction. Initial symptoms matched yours, engine overheating and check engine warnings. The root cause turned out to be a failing coolant temperature sensor which caused incorrect readings, leading to improper fuel mixture and eventual power loss. This created extra stress on the bypass valve. The repair required replacing both the sensor and the bypass valve to restore proper engine function. This was a serious repair job since continued operation could have led to engine damage. The symptoms you describe strongly suggest getting it checked soon, as overheating can quickly escalate to major engine problems. The low mileage on your Bora actually increases the likelihood of sensor issues, as extended periods of inactivity can affect electronic components. Worth noting that these cooling system issues were common in that generation of engines. Recommend getting a full cooling system diagnostic before driving extensively. The fuel efficiency will likely improve significantly once the system is operating correctly.

Thanks for the detailed explanation about your Golf issue. This sounds exactly like what I am experiencing with my Bora, including the power loss you mentioned. I had no idea the air intake and coolant systems were so interconnected. Did the repair completely solve your overheating issues? Would be great to know how much you ended up paying and if any other problems showed up afterwards. Just trying to get an idea of costs before heading to the shop.

The repair totally fixed the overheating and engine stalling issues. After discovering the coolant temperature sensor was the root cause, replacing it solved all problems including the bypass valve malfunction. The vacuum system returned to normal operation once the sensor was working correctly. The great news was the repair came at no cost since it was classified as a consequential error from the faulty sensor which was still under extended warranty. The shop handled all warranty paperwork, making the process straightforward. Its been six months since the fix and the engine runs perfectly, no more power loss or temperature warnings. Fuel consumption actually improved once everything was working properly. The cooling system now maintains ideal temperature even during longer drives. Make sure to mention these symptoms to your mechanic, especially the connection between the temperature readings and power loss. Getting the full diagnostic done is crucial for catching any related issues in the vacuum system before they cause additional problems.

Thanks everyone for the suggestions. I finally took my Bora to a mechanic last week and the diagnosis matched what was discussed here. The engine overheating was indeed triggered by a faulty coolant temperature sensor. The repair cost came to 450€ including parts and labor. The mechanic also found minor issues with the air intake system which were fixed during the same visit. The bypass valve was actually fine, just responding to incorrect sensor data. The car runs great now, no more check engine light or temperature warnings. Engine stalling is completely gone and it feels much more responsive. Glad I caught this before any serious damage occurred. For anyone facing similar symptoms, definitely worth getting it checked early. The whole repair took just one day and saved me from potential major engine problems down the line.