VW Up Coolant Loss Mystery: Common Leak Symptoms Explained

Had a similar issue with my 2021 VW Polo last summer. Have some experience working on cars, mainly basic maintenance and troubleshooting. The symptoms you describe match exactly what I experienced, check engine light, disappearing coolant, but no visible leaks. Initially suspected air pockets in the cooling system, but the issue persisted. Took it to my regular workshop where they found a faulty sensor connection near the water pump. The plug had corroded, causing incorrect readings and system warnings. Total repair cost was 95€ including diagnostics and fixing the connection. Before spending money at a workshop, you might want to: 1. Check all visible hoses for signs of wear 2. Inspect around the water pump for weeping 3. Look for white exhaust smoke (possible head gasket issue) 4. Monitor if engine overheating occurs Could you share: Current mileage? How often are you adding coolant? Any unusual engine temperature readings? Notice any sweet smell from the engine bay? This would help narrow down if your issue matches what I experienced or points to something different.

Thanks for the detailed response. Currently at 24674km and had the last service just 2 weeks ago. After checking more thoroughly, I notice a sweet smell near the radiator cap when the engine is warm. Adding radiator fluid about every 2 weeks, roughly 500ml each time. The cooling fan seems to run more frequently than before, especially in slow traffic. The engine temperature gauge stays normal most of the time but occasionally creeps up when idling. Think I should get the cooling system pressure tested before making assumptions about the head gasket. Will check those hose connections you mentioned too. Any chance the water pump could be failing this early? Seems unusual with such low mileage on a new car.

Based on your latest description, these symptoms sound different from what I experienced with my sensor issue. The sweet smell near the radiator and increased cooling fan activity point to a possible coolant leak that is evaporating due to engine heat. In my Polo, the faulty sensor connection caused false readings but did not result in actual coolant loss or sweet smells. Your 500ml coolant loss every 2 weeks is concerning and definitely needs attention. The water pump could be failing early, while uncommon at 24674km, it does happen. Look for weeping around the pump shaft seal. My initial sensor problem masked a developing water pump issue that showed up later, causing similar symptoms to what you describe. Since you are still under warranty, strongly recommend getting this checked at the dealer. The coolant reservoir level changes combined with the sweet smell and increased cooling fan operation suggest an actual leak rather than just a sensor problem like I had. A pressure test will quickly identify if there is a leak in the system. The rising temperature at idle particularly concerns me as this was not present in my sensor-related case.

Thanks everyone for the suggestions. After your feedback, I took it to the dealer today. They pressure tested the cooling system and found a hairline crack in the coolant reservoir. The continuous loss of coolant was causing the engine temperature fluctuations and increased fan activity. The sweet smell was from coolant vapor escaping through the crack. The total repair was covered under warranty since the car is only 8 months old. They replaced the coolant reservoir, performed a system flush, and rechecked all hose connections. No issues with the water pump or head gasket. Engine temperature now stays steady and the cooling fan operates normally. No more check engine light or coolant loss after driving 200km. Definitely glad I did not ignore the symptoms or try temporary fixes. Still monitoring the coolant level daily just to be safe, but everything seems back to normal. Really appreciate all the input that helped identify the problem area.