RS7 Coolant Loss Despite Top-Ups Points to HG Failure

Having dealt with similar cooling system issues on my A6 3.0T, this sounds like a possible failing cooling fan control module or a faulty coolant level sensor. When my coolant light started flashing intermittently, the issue turned out to be more complex than just low coolant. The root cause was a deteriorating radiator cap and hairline cracks in one of the radiator hoses, causing the system to lose pressure. This led to coolant loss through seepage rather than an obvious leak. The check engine light triggered because the cooling system was unable to maintain proper pressure. A proper diagnosis revealed multiple issues: Failed radiator cap pressure seal, Coolant leak from the radiator hoses near the clamps, Damaged wiring connector at the coolant level sensor This required complete replacement of the radiator hoses, a new radiator cap, and rewiring of the sensor connector. It was a serious issue that needed immediate attention to prevent potential engine damage. The symptoms match closely with what you are describing. Would strongly recommend getting a pressure test done on the cooling system before assuming its a head gasket issue. Visible coolant leaks are not always present even when the system is losing coolant.

Thanks for the detailed reply about the cooling system issues. My situation does sound very similar, especially the part about the coolant reservoir problems and sensor wiring. I had the complete repair done and it fixed the engine overheating concerns, though keeping an eye on the cooling fan operation just to be safe. Would you mind sharing what the total repair cost was in your case? Also curious if you encountered any other cooling-related problems after getting it fixed?

After getting my car checked by a certified mechanic, the coolant level issue was completely resolved. The main problem turned out to be much simpler than initially feared, just a faulty cable connection to the coolant level sensor. The repair cost was 95 Euro, which included diagnostic testing and fixing the connection. Unlike more serious cooling system problems involving the water pump or head gasket, this was a straightforward fix. The radiator fluid level now stays consistent, and I have not experienced any other cooling-related issues in the months since the repair. The warning lights have stayed off, and the cooling system maintains proper pressure. My advice would be to keep monitoring your coolant levels regularly, even though the problem is fixed. A properly functioning cooling system should maintain stable radiator fluid levels without needing frequent top-ups. If you notice any changes, getting it checked early can prevent more expensive repairs down the line. In my case, catching the issue early meant avoiding potential damage to other cooling system components.

Just took my car to get fixed today after seeing all the suggestions here. The mechanic found exactly what was suspected, a bad sensor connection and a worn radiator cap that wasnt holding pressure. Total bill came to 140 Euro for parts and labor, plus they did a complete cooling system pressure test to make sure there were no other issues. Really glad I went in before it became something more serious like a water pump failure or worse. The coolant reservoir level has stayed steady since the repair and both warning lights are now off. The cooling fan is working normally too, which is a relief. Going to follow the advice about monitoring the coolant levels regularly just to be safe, but so far everything is working perfectly. Much better experience than my previous dealer visits and definitely less expensive than I feared it might be.