Thermostat OEM Volkswagen or Motorcraft

I used a motorcraft RT-1139 thermostat. Comes with a jiggle valve to help bleed air already installed and cost me 8 bucks. You won’t find any place that says they fit other than some forum posts but they do indeed work, I installed one on my MJ with the only issue being me not refilling the radiator after dumping all the coolant.

I requested they use only Motorcraft thermostat, because I knew there was a part # update. Threw the updated Motorcraft one in and it solved the issue.

Soon as i bought Motorcraft all was normal again

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.

Make sure you use the motorcraft thermostat.

Go with the Motorcraft thermostat as it has a rubber seal on the outside edge.

Parts 03F-010-501-B Sensor 04E-121-113-G

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.

I’ve had a Motorcraft thermostat fail after 100mi on my Ford