Audi S5 Radiator Fan Failure Causes Engine Overheating

Had a similar issue on my 2011 Audi S4 last summer. The engine cooling system was malfunctioning due to a faulty thermal switch, which prevented the radiator fan from activating at the correct temperature. The fan motor would only kick in when the engine was severely overheating. The diagnostic revealed two problems: a defective speed sensor and a failing thermal switch. This combination caused irregular fan operation and engine temperature fluctuations. It was a serious issue that required immediate attention since continued driving could have led to engine damage. The repair involved replacing both components and performing a full cooling system inspection. The fan noise returned to normal after the fix, a subtle whirring at idle that increases with engine temperature. These cooling system issues are relatively common on this engine platform. Getting it checked quickly is important. A proper diagnosis will determine if its the thermal switch, fan motor, or speed sensor causing the problem. These symptoms should not be ignored as they can lead to major engine damage if left unaddressed.

Thanks for sharing that experience. I actually encountered almost the exact same cooling issue on my S5. The radiator fan would barely spin and the engine kept running hot, just like you described. The thermal switch ended up being the main problem, though my fan blade also had a small crack that was causing weird fan noise. Did you keep track of the repair costs? And has everything been working properly since the fix? Just wondering if any other cooling-related issues came up afterward.

The repairs worked out great on my S5. After spending 250 Euro to fix the speed sensor, the engine cooling system has been running perfectly. The car radiator fan now kicks in exactly when it should, and the fan noise is back to that normal gentle hum at idle. Since having the mechanic address the defective parts last summer, I have not experienced any additional cooling problems. The fan motor engages properly with temperature changes, and engine temperatures stay consistently in the normal range. It was definitely worth getting it fixed properly rather than letting it continue. Running with a faulty cooling system can cause serious engine damage, so the repair cost was a good investment in preventing bigger issues down the road.

Thanks for the input. I finally got my S5 checked out yesterday. The mechanic found both the thermal switch and cracked fan blade, just like mentioned here. Total bill came to 420 Euro including parts and labor, but the cooling system is working perfectly now. The engine temperature stays steady and the radiator fan kicks in normally. Best part is hearing that proper fan noise again when idling, its amazing how you dont notice these things until they are fixed. No more check engine light either. Feels good knowing I caught it before any serious engine damage occurred. The mechanic showed me the old parts and explained everything clearly. Much better experience than my previous repair shop.