RS4 Temperature Control Nightmare: Thermostat Alert

Had the same issue on my 2009 S5 last winter. The erratic temperature behavior exactly matched your symptoms, slow warmup followed by overheating cycles. The root cause was a faulty map thermostat, which was causing incorrect coolant flow regulation. This component is part of the cooling system and works with the temperature sensor to manage engine temperature. The defective thermostat was either staying stuck open or closed, preventing proper temperature control. This is a serious issue that needs immediate attention since continuous overheating can severely damage the engine. During the repair, the mechanic also found a minor coolant leak at one of the connecting hoses. The cooling fan was working correctly, but the system couldn't maintain stable temperature due to the bad thermostat. The repair involved: Replacing the map thermostat, Pressure testing the entire cooling system, Replacing coolant and bleeding the system, Checking the water pump for proper operation Watch for these warning signs: Temperature gauge moving erratically, White smoke from exhaust, Sweet smell from engine bay, Low coolant levels Best to have it checked soon as continuing to drive risks engine damage.

Reading your experience sounds very familiar, dealing with the exact same temperature problems on my RS4 about 6 months ago. The map thermostat ended up being the culprit too, plus I needed a new temperature sensor. The cooling fan and water pump checked out fine thankfully. Getting those parts replaced resolved the engine overheating issues completely. My RS4 now warms up normally and maintains steady temperature even on longer drives. How much did you end up paying for the full repair? And has everything been running smoothly since the fix? Just curious if any other cooling system problems popped up later.

Thanks for the follow-up about your RS4. Glad to hear you got the same issue resolved. After my thermostat cooling circuit repair, everything has been running perfectly for over a year now. The temperature stays consistent and the engine warms up normally, just as it should. The total repair came to 350 Euro for fixing the defective map thermostat. This is pretty standard pricing from what other owners have reported for similar cooling system repairs. The mechanic did a thorough check of the entire cooling system during the fix, and no other problems have emerged since then. Its crucial to address engine overheating issues quickly, as you did. Letting a faulty thermostat go unfixed can lead to serious engine damage. Regular coolant system maintenance and keeping an eye on temperature readings can help catch these problems early.

After dealing with my temperature control issues, I finally got everything sorted at a reliable mechanic. The whole experience was actually better than expected. The shop did a complete cooling system diagnostic and found both a failing thermostat housing and a worn temperature sensor. They pressure tested everything and also spotted a small coolant leak from one of the hoses that I hadnt noticed before. Total bill came to 420 Euro for parts and labor, which included: New map thermostat, Temperature sensor replacement, Coolant hose repair, Fresh coolant and system flush The car runs perfectly now, no more temperature fluctuations or overheating concerns. Engine warms up normally and maintains steady temperature even on longer drives. Really glad I got it fixed before any serious damage occurred. Big thanks to everyone who shared their experiences. The advice helped me know exactly what to look for during the repair process.