A6 Temperature Woes Point to Cooling System Issues

I had a similar issue with my 2006 A4 2.0T last winter. With some experience working on cars, I can share what worked for me. The symptoms you describe are familiar, inconsistent temperature readings and slow warm-up times. Initially thought it was a restricted airflow problem with the radiator grille, but it turned out to be simpler. A blown fuse was causing the temperature sensor to malfunction, triggering both the erratic readings and check engine light. The fix was straightforward, 52 Euro at my regular workshop, mainly labor costs to diagnose and replace the fuse. They also performed a cooling system check to ensure there were no underlying issues with the automotive cooling components. However, your case might be different since these symptoms can have multiple causes in Audi engines. Could you share: Any unusual noises from the engine bay? Does the car actually overheat or just show incorrect readings? Have you noticed any coolant leaks? When was your last cooling system maintenance? This information would help determine if you are dealing with a simple electrical issue like mine or something more complex in the cooling system.

Had the last service done at 109000 KM. Thanks for the input. No unusual noises from the engine bay, but I notice the engine cooling fan runs more frequently than before. The temperature gauge fluctuates between normal and cold, never showing overheating. No visible coolant leaks around the engine or under the car. The thermal management system was last checked during routine maintenance about 600 KM ago. The mechanic did mention the coolant level was slightly low but within acceptable range. Given the erratic temperature behavior and the check engine light, I will have it properly diagnosed to rule out any serious issues with the engine cooling system. Will update once I get more information from the shop.

Thanks for the additional details about your A6. The frequent cooling fan operation combined with fluctuating temperature readings does suggest a different issue than what I encountered with my A4. Given that your coolant level was slightly low during the recent service, the thermal management system might need attention. While my case was resolved with a simple fuse replacement, your symptoms point toward potential issues with either the thermostat or temperature sensors. The restricted airflow theory through the radiator grille seems less likely now, especially since you are not experiencing actual overheating. A malfunctioning thermostat would explain both the erratic temperature readings and the increased fan activity. From my repair experience, thermostats on these engines typically cost between 150-200 Euro for parts and labor. If it is indeed a sensor issue like mine was, you might be looking at a lower repair cost. Would recommend getting the diagnostic trouble codes read before proceeding with any repairs. The check engine light should provide specific information about whether this is a sensor, thermostat, or other engine cooling component issue.

Based on your findings and the previous replies, I will take my car to the shop tomorrow. The symptoms really point toward either the thermostat or temperature sensors rather than a grille restriction issue as I initially thought. The frequent cycling of the engine cooling fan plus the erratic temperature readings without actual engine overheating make more sense now. Since the thermal management system was checked recently and showed only slightly low coolant, a faulty thermostat seems the most likely culprit. Appreciate the cost estimate of 150-200 Euro for thermostat replacement. This helps set realistic expectations for the repair. Will definitely have them pull the diagnostic codes first to pinpoint whether its a sensor issue or thermostat problem before authorizing any work. Planning to update this thread once I get the actual diagnosis and repair completed. This discussion has been really helpful in understanding the potential causes behind these temperature-related issues.