VW Phaeton Cooling System Troubles & Solutions

Having dealt with a similar issue on my 2006 VW Passat 2.0 TSI, I can share some relevant experience. The symptoms you describe match what I encountered, though I have moderate experience with car repairs. Initially, I also thought the radiator grille was causing airflow problems leading to engine cooling issues. However, after taking it to the workshop, they discovered a blown fuse controlling the cooling system sensors. The erratic temperature readings were caused by this faulty fuse disrupting the signal from the temperature sensors to the ECU. The repair was straightforward, replacing the fuse and running diagnostics to clear the check engine light resolved the automotive cooling issues completely. Total cost was 52€ including diagnostics and parts. To provide more specific guidance for your case: What engine variant does your Phaeton have? Are you noticing any coolant loss? Does the car overheating occur more during city driving or highway speeds? Have you checked the coolant level and condition? These details would help determine if your issue matches what I experienced or if there might be other underlying problems needing attention.

My Phaeton has the W12 6.0L gasoline engine and just had its service at 131178km. After reading your reply, I checked the coolant level and its dark green color suggests contamination. The overheating mainly occurs during city driving. No visible coolant loss, but the thermal management system seems more erratic in slow traffic. The engine temperature fluctuates between normal and high even when the cooling fans are running at full speed. Based on your experience with the fuse, I will have that checked first before considering more extensive repairs to the cooling system.

Thanks for those details about your W12 Phaeton. My Passat case was indeed similar, but after hearing about your coolant condition, I suspect your issue might be more complex than just a blown fuse. The dark green coolant color often indicates contamination in the cooling system, which can cause radiator blockage and irregular temperature readings. In my case, after fixing the initial fuse problem, I later discovered partial blockage in the radiator passages. When my engine cooling problems persisted during city driving, the workshop found that contaminated coolant had created restrictions in the cooling passages. The full repair included: Cooling system flush, New coolant, Thermostat replacement, Radiator pressure test Total repair cost was 680€, significantly more than just the fuse replacement, but it completely resolved the restricted airflow and temperature fluctuations. Given your W12s complex thermal management system, I recommend getting a full cooling system diagnostic. The contaminated coolant could be causing multiple issues that need addressing before more serious engine damage occurs.

I appreciate the detailed explanation about the coolant system issues. Based on your experience with similar automotive cooling problems, I will schedule a complete diagnostic focusing on both the electrical and mechanical aspects of the cooling system. The contaminated coolant in my W12 definitely seems more serious than just a fuse problem. Your description of the radiator blockage matches my symptoms perfectly, especially the erratic behavior during city driving when the engine cooling demands are highest. I checked the radiator grille area more thoroughly and noticed some debris buildup, but that seems secondary to the internal cooling system contamination. Will have the shop do the complete flush and inspection you suggested, including: Cooling system flush, Fresh coolant replacement, Thermostat check, Full pressure testing, Electrical diagnostic for the temperature sensors The 680€ repair cost you mentioned seems reasonable for the complete service. Car overheating issues with these engines can lead to much more expensive damage if left unchecked. Will update once I have the work done and know what they find. Thanks for helping me narrow down the likely causes.