Audi SQ8 Cooling System Chaos: Hot Yet Cold Engine

Having medium experience with Audi repairs, I encountered a very similar issue with my 2018 Audi SQ7. The engine overheating symptoms and slow warm-up behavior matched exactly what you describe. After monitoring the temperature sensor readings, my workshop diagnosed a defective map thermostat in the coolant system. The erratic cooling fan behavior was actually a response to incorrect temperature signals. The repair involved: Complete diagnosis of the cooling system, Replacement of the map thermostat, System bleeding and coolant refill, Testing temperature control under various conditions Total cost was 350 Euro and it completely resolved both the overheating and the slow warm-up issues. The engine temperature has been stable ever since. To provide more specific advice: What engine variant does your SQ8 have? Also, have you noticed any changes in coolant consumption? This information would help determine if your case is similar to what I experienced. While waiting for a proper diagnosis, monitor your temperature gauge closely and avoid high-load driving conditions to prevent potential engine damage from overheating.

Last service done at 90000 KM just 2 months ago. Thanks for sharing your experience. The cooling fan operation you described sounds identical to my situation. After reading your reply, I checked the engine temperature readings using an OBD scanner which shows inconsistent values compared to the dashboard gauge. Given these conflicting temperature sensor readings, a malfunctioning thermostat in the cooling system seems the likely culprit, especially since there are no visible coolant leaks. I have the 4.0L TFSI gasoline engine. No noticeable coolant consumption changes so far. Will definitely have the workshop check the map thermostat and temperature sensors during diagnosis.

I can confirm that the thermostat housing issues are quite common with these 4.0L TFSI engines. After fixing mine, I learned more about the cooling system design and how the map-controlled thermostat works. The OBD scanner readings you mentioned match what I saw, the discrepancy between dashboard and actual temperature readings is a telltale sign of thermostat malfunction. The cooling system in these engines is quite sophisticated, and when the thermostat starts failing, it often causes these mixed signals. In my case, the workshop also found the wiring to the thermostat was slightly corroded, which contributed to the erratic cooling fan behavior. Worth having them check this during diagnosis. Since your symptoms are identical and you have the same engine, I strongly suspect you are dealing with the same issue. While 350 Euro was my repair cost, prices may vary depending on current parts availability. One tip from my experience: make sure they properly bleed the cooling system after repair. Any trapped air can cause similar symptoms to return.

Thanks for confirming the similar symptoms with your SQ7. The inconsistent OBD temperature readings definitely point toward thermostat failure in the cooling system. I will book a workshop appointment next week and have them focus on the map thermostat, wiring connections, and complete system diagnosis. Good point about the cooling system bleeding procedure. I will specifically ask them to ensure proper bleeding after the repair to avoid any recurring engine overheating issues. The 350 Euro repair cost seems reasonable considering the complexity of the temperature control system in these engines. The corrosion detail you mentioned is particularly helpful since my car has seen some wet weather lately. Will have them inspect the thermostat wiring connections as well. For now, I am keeping a close eye on the temperature gauge and avoiding any high-stress driving until the repair is completed. Really appreciate the detailed feedback, it helped narrow down the likely cause and saved me some diagnostic time.