RSQ3 Cooling System Drama: Thermostat Troubles Exposed

Had a similar issue with my Q3 2017 2.0 TFSI last winter. Have some experience working with Audi engines and cooling systems. The symptoms match exactly what I experienced, inconsistent temperature readings and the engine taking forever to reach operating temperature. The cooling fan was working overtime once warm. Initially thought it might be a failing water pump or coolant leak. After diagnostic testing, the workshop confirmed a defective map thermostat was causing the erratic temperature control. The repair involved replacing the thermostat and doing a complete cooling system flush. Total cost was 350 Euro including parts and labor. The fix completely resolved the temperature fluctuations. Engine now warms up normally and maintains steady operating temperature, even during extended drives. To provide more specific advice for your case: What engine variant does your RSQ3 have? Are you noticing any coolant loss? Does the temperature sensor show consistent readings or does it fluctuate? Have you noticed the cooling fan running more frequently than usual? These details would help compare if your issue matches what I experienced.

Based on my recent service at 190136 KM, I think your diagnosis about the thermostat matches my experience. The mechanic found that engine overheating was happening after prolonged warm-up periods. There were no visible coolant leaks in my case. Initial tests with the cooling fan operation and thermostat function showed intermittent behavior. The final fix required replacing both the thermostat and temperature sensor, costing around 425 Euro for parts and labor. The temperature now stabilizes much faster and maintains proper levels during all driving conditions. I recommend having your coolant system pressure tested first to rule out any leaks before replacing components. Would you mind sharing your temperature gauge readings when the issue occurs? This could help confirm if we had the same problem.

The temperature readings I experienced were quite similar to what you described. When the issue was at its worst, my gauge would hover around 70-75C during warm-up for much longer than normal. Once finally warmed up, it would spike toward 105-110C during regular driving. The thermostat housing replacement definitely fixed these erratic temperature swings. Since the repair, warm-up time is back to normal (about 5-7 minutes) and the temperature stays steady at 90C, which is exactly where it should be for our engine. One additional observation from my experience: the cooling fan behavior normalized after the thermostat replacement. Before the fix, it would kick in seemingly at unusual intervals, even during cold starts. Now it only activates when actually needed. This inconsistent temperature control can definitely stress other cooling system components if left unchecked. Getting the thermostat replaced at the first sign of these symptoms is worth the investment to prevent potential engine damage from overheating.

Thanks for sharing those temperature readings. Now I'm even more confident we dealt with identical issues. During my worst episodes, the gauge showed exactly those ranges, taking forever to get above 70C, then suddenly climbing past 105C during normal driving. After the thermostat and sensor replacement, my temperature control has been perfect for the past 7 months. The engine now consistently reaches 90C within 5-6 minutes and stays there. No more erratic cooling fan behavior either, which was definitely a symptom of the faulty thermostat trying to compensate. The pressure test was a smart first step to rule out coolant leaks. In my case, the cooling system held pressure perfectly, which helped confirm the thermostat as the culprit. Based on both our experiences, these symptoms seem like a common failure point for this engine. Would you mind sharing how many kilometers you had on your thermostat when it failed? Might help establish a typical service life for this part.