VW Beetle Coolant Mystery: Fix Before Engine Damage

Having some experience with VW repairs, I dealt with a similar issue on my 2015 VW Golf. The symptoms were nearly identical, check engine light and coolant problems without visible leaks. After taking it to the workshop, they found the culprit was a faulty sensor connection near the coolant reservoir. The plug had corroded, causing false readings and system errors. The repair cost was 95€, which included cleaning the connection points and replacing the damaged plug. Before the fix, I was concerned about potential air pockets in the cooling system, but thankfully the radiator fluid circulation was working properly. The radiator hoses were also inspected and found to be in good condition. To better assist with your situation, could you share: Current coolant consumption rate, Any unusual engine temperature readings, Whether the coolant level drops gradually or suddenly, If the head gasket has ever been replaced, Approximate mileage on your Beetle These details would help determine if your issue matches what I experienced or if it might be something different. Until you can get it checked, keep monitoring the coolant level and engine temperature closely.

Thanks for sharing your experience. My Beetle just hit 141368km and started showing these symptoms right after the latest service. The coolant level drops gradually, about 1cm per week. The temperature gauge stays normal during regular driving, but I notice a slight increase during idle. The water pump was replaced at 90000km, so I doubt thats the issue. I checked the radiator cap and its sealing properly. No white smoke from exhaust or sweet smell, so head gasket seems fine. Think I should have the radiator hoses pressure tested first, or go straight for a full cooling system diagnostic?

Thanks for those details, the symptoms sound fairly similar to what I experienced with my Golf, though your coolant loss rate is a bit concerning. A gradual coolant loss like you describe, combined with normal operating temperatures, often points to a small leak that evaporates before forming visible drips. When my Golf had cooling system issues, I learned that radiator hoses can develop tiny cracks that are hard to spot visually. Given the mileage and symptoms, I would recommend going for the full cooling system diagnostic. While pressure testing the radiator hoses is helpful, the complete diagnostic can catch issues with: Internal leaks not visible from outside, Air pockets in hard-to-reach areas, Radiator fluid circulation problems, Minor cracks in the expansion tank, Cooling fan operation during idle The full diagnostic cost me 150€ but saved money in the long run by identifying all potential issues at once. Just monitoring the coolant level until the test is done should be fine since your temperature readings are still normal.

Thanks for the detailed response. That makes sense about the full diagnostic being more thorough. I'll schedule that instead of just the pressure test to catch any hidden issues. With the gradual coolant loss and slight temperature increase at idle, I dont want to risk engine overheating by only doing partial checks. I called a shop that specializes in VW cooling systems and they can get me in next week. The diagnostic costs 165€ but includes pressure testing, leak detection dye, and a full system inspection. They mentioned theyll check the radiator cap and all hoses too. Until then, I'll keep an eye on the coolant level and temperature gauge. Really hoping its just a minor leak and not anything major with the head gasket or radiator. Will update once I get the results back from the shop.