VW Golf TDI Coolant Loss & CEL Mystery Needs Fixing

Had a similar issue with my 2006 VW Passat TDI. The coolant loss combined with check engine warnings pointed to multiple problems in the cooling system. The radiator cap was not maintaining proper pressure, which caused air pockets to form. After replacing it, coolant still disappeared. Further inspection revealed hairline cracks in the head gasket, allowing coolant to leak internally. This explained both the low coolant levels and engine codes. The head gasket failure is a serious issue that can lead to engine overheating and internal damage if not addressed. In my case, the water pump also showed signs of wear, so both components were replaced during the repair. These TDI engines are known for developing cooling system issues around this mileage range. Would suggest getting a pressure test done on the cooling system first. This can pinpoint if the issue is external leaks from hoses or internal problems like the head gasket. The symptoms match classic head gasket failure patterns in these engines.

Thanks for the detailed response about the cooling system issues. The symptoms sound exactly like what I am experiencing. My mechanic checked the radiator fluid level but did not perform a pressure test. I will definitely ask for one on my next visit. How much did you end up paying for the total repair after they found the cracked head gasket? Also curious if you had any other cooling-related problems after fixing everything? My coolant reservoir still seems to lose fluid faster than normal, and I want to make sure I address all potential issues at once.

Good news, got my cooling issues fully sorted now. Turns out the main problem was much simpler than a head gasket failure. The mechanic found a faulty cable connection to the cooling fan that was causing the system to malfunction. This explained both the check engine light and why the coolant reservoir was losing fluid. The repair only cost 95€ to fix the connection, much less than I initially feared. Since having this done, the coolant level has remained stable with no more unexplained loss. The cooling system is now maintaining proper pressure and temperature. For your situation, definitely get that pressure test done. While my issue was electrical, air pockets in the system can cause similar symptoms. A proper test will show if you are dealing with actual leaks or component failures. The cooling system in these engines needs to be working perfectly to avoid more serious problems down the line. Make sure they check all electrical connections to the cooling components too, as sometimes the simple fixes get overlooked when searching for major mechanical issues.

Thanks for the helpful advice. Wanted to update on what happened with my Golf TDI cooling problems. Took it to a different mechanic who specializes in VW engines. First thing they did was a proper pressure test of the entire cooling system. Found the water pump was actually cracked and leaking coolant slowly. The original mechanic missed this completely. Total repair came to 320€ including a new water pump and fresh coolant. They also replaced two worn radiator hoses while they were at it since the rubber was starting to deteriorate. The check engine light finally turned off after the repair. Been driving for 2 weeks now and the coolant level has stayed consistent. Engine temperature reads normal even during longer drives. Really glad I got a second opinion instead of jumping straight to major repairs like a head gasket replacement. Big lesson learned about getting a complete diagnostic test done first. Sometimes the obvious signs point to something worse, but it pays to have everything properly checked before spending money on unnecessary repairs.