Thermostat OEM Volkswagen or OEM Nissan

It has been two weeks since the repair without issues, so I am going to call this one solved. If I was paying for this out of pocket in the future, I would only replace the thermostat and not the pump as that is what was closing and causing the issue.

Since going with the OEM thermostat, my temp gauge has stayed pinned just below the middle of the gauge, even towing campers and heavy loads on hot days.

Only an OEM Thermostat fixed it.

I did the timing belt water pump thing on my MK4 last year, and shortly after the test drive with fresh genuine VW antifreeze and while patting myself on the back for a job well done it occurred to me that I hadn't changed the thermostat. Sure enough a month or so ago when the first of the really cold whether started around here the temp gauge would only get to about halfway to normal during a trip to town and back. I tried the ol' cardboard in the grill routine for a couple of days until I got a chance to change the thermostat and that brought things back to normal.

I had this exact issue with 3 aftermarket thermostats that were opening too early. Bought one from Nissan and my temps went back to normal

OEM Nissan, but slightly more conservative with cooling.

Replacing the Thermostat with a OEM part has solved the issue (with coolant flush) from a dealership.

I have owned my B6 since new and had the thermostat replaced under Warranty around 36,000 miles, at that point the slow warm up was causing the MIL to illuminate with a error that basically said warm up outside specification.

After getting mine back together, and filling it back up with coolant, i found the new thermostat from the dealership was stuck wide open and the car wouldn’t get over 110*F.

mine is also a problem an my car is 1.5 yrs old. Sometimes the temp gauge acts as if it is -40C outside even if it is a couple degrees above freezing. Often the car will take 4-5minutes to get near base idle when it is cool outside, but when it's really cold, sometimes it takes 30seconds and there is no way it's warmed up. Can also smell coolant anytime I open the hood. Sad.