S3 Engine Light + Coolant Issues Signal Costly Trouble

Had similar issues with my 2010 A3 2.0T. The check engine light combined with coolant warnings pointed to a serious cooling system problem. The coolant leak was traced to a failing head gasket, which was allowing coolant to mix with engine oil. The radiator fluid level kept dropping despite no visible leaks underneath the car. A pressure test revealed the issue, coolant was escaping through the compromised head gasket. The cooling fan was working properly and the radiator cap held pressure, so those common failure points were ruled out. In cases like this, continuing to drive risks major engine damage if the cooling system cant maintain proper temperature. The repair required removing the cylinder head to replace the head gasket and machine the mating surfaces. This is definitely a job for an experienced shop with proper diagnostic equipment and repair capabilities. Would strongly recommend getting it checked soon, as head gasket failures tend to get progressively worse and can lead to complete engine failure if left untreated. Engine overheating and coolant mixing with oil are serious red flags that need immediate attention.

Thanks for the detailed response about your A3 cooling system issues. My symptoms sound identical, especially the mysterious coolant loss without visible leaks. Getting it checked this week to avoid bigger problems. Quick question, do you recall the total repair cost for your head gasket job? Also wondering if youve had any air pockets or coolant reservoir problems since the repair? My coolant warning light still comes on occasionally even after topping up the reservoir.

After fixing my A3 cooling system, I have good news that might help. My issue turned out much simpler than a head gasket failure. The mechanic found the coolant level was consistently low due to a faulty sensor connection. The fix was straightforward, just needed to repair a damaged cable connection to the coolant level sensor. Total cost was 95 Euro for parts and labor. Since the repair, the warning lights have completely stopped, and the cooling system maintains proper levels without any issues. No more problems with air pockets in the system or false coolant warnings. The engine runs at normal temperature, and I haven't had to add any radiator fluid since the repair. If your symptoms match what I experienced, it might be worth having them check the sensor connections first before assuming worst-case scenarios. Just make sure your mechanic does a proper pressure test of the cooling system to rule out actual coolant leaks. This way you can be confident whether its a real leak or just a sensor issue like mine was.

Thanks everyone for sharing their experiences. Took my car to a new mechanic yesterday and wanted to update on the outcome. Turns out my issue was a combination of a cracked radiator hose and trapped air pockets in the cooling system. The mechanic performed a thorough pressure test and found the leak right away. They also noticed the radiator cap wasnt sealing properly, which explained the occasional air bubbles. Total repair cost came to 180 Euro including new radiator hoses, cap, coolant flush, and labor. Much better than I feared after reading about potential head gasket issues. Car has been running great for the past few days with no warning lights or coolant loss. Really glad I got it checked quickly instead of driving around worried about it. The cooling fan cycles normally now and the temperature stays steady. What a relief to have it sorted without major engine work.