Audi SQ5 Cooling System Acts Completely Backwards

Had the exact same symptoms on my 2010 Audi S4 last year. The erratic temperature control behavior points strongly to a defective map thermostat, which is a common issue on these engines. The strange combination of slow warm-up and overheating happens because the map thermostat fails to regulate coolant flow properly. When the temperature sensor readings are incorrect, the ECU gets confused about when to open and close the thermostat housing. The repair required replacing both the thermostat and housing assembly since they are integrated. While doing this work, the mechanic also inspected the water pump as it can contribute to engine overheating issues. The entire cooling system needed to be pressure tested afterward. This turned out to be a serious repair that required specialized diagnostic equipment. The symptoms progressively worsened until fixed, and continuing to drive risked engine damage from overheating. The fix completely resolved both the warm-up delays and overheating issues. Given your symptoms and mileage, recommend having a professional shop check the map thermostat and temperature sensor readings before the problem escalates.

Thanks for sharing your experience. Those symptoms sound exactly like what I dealt with. Since getting my map thermostat and housing replaced, the temperature has been rock solid. Curious though, do you remember roughly what you paid for the full repair? Also, have any cooling system issues popped up since the fix? In my case, having the water pump checked during the thermostat housing replacement was smart preventive maintenance, since the coolant leak could have damaged multiple components. Getting that temperature sensor readings verified by a pro shop definitely saved me from bigger problems down the road.

Glad to hear you got it sorted out. After my thermostat cooling circuit motor was diagnosed as defective, the repair totaled 350 Euro for parts and labor. That included a complete inspection of the cooling system and pressure testing to ensure no other components were compromised. Since fixing the defective map thermostat, my engine temperature has stayed perfectly regulated with no coolant leaks or overheating issues. Going on 14 months now with zero cooling system problems. The proper diagnosis and repair really does make all the difference. The preventive water pump check during thermostat replacement is indeed smart maintenance. A failing pump can create similar symptoms and cause engine overheating, so having both components inspected together saves time and prevents future issues. Good to hear you also had the temperature sensor readings professionally verified. When the thermostat fails, it can sometimes damage other parts of the cooling system if left unchecked for too long.

Thanks for the helpful advice. Just wanted to close the loop on my experience. Finally got the car properly diagnosed and fixed last week. The mechanic confirmed the map thermostat had failed, causing the erratic temperature control. The total repair came to 420 Euro, which included replacing the thermostat housing assembly and a thorough cooling system inspection. They found a small coolant leak near the water pump but caught it early before any serious damage occurred. Been driving for about a week now and the temperature gauge stays perfectly steady. No more cold start issues or overheating problems. The engine warms up normally and maintains consistent temperature even in stop-and-go traffic. Really glad I had the temperature sensor readings checked professionally instead of continuing to drive with the problem. Looking back, the symptoms were classic signs of a failing thermostat. Lesson learned about addressing cooling system issues promptly.