Thermostat MISHIMOTO or OEM Volkswagen

It’s now got an 85°c Mishimoto thermostat. Took it out today and got it up to temp and did multiple 0-85mph pulls. The new thermostat opens at 85°C/185°F. Under load the coolant never registered above 197°F!!!!

Mishimoto has a great thermostat plus it has a lifetime warranty

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've got a 13 sport with 135k miles on it. Only ever done oil changes, spark plugs, 12v battery and a thermostat. Other than that it’s been stupid reliable.

Sounds like your water pump is working, but maybe your thermostat is stuck closed? Have you tested the thermostat?

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

Forget about the Mishimoto thermostat. The OEM thermostat is way more reliable and does the job.

I put the mishimoto 160* in hot water to test it out. Lo and behold, wax started seeping out.

I had 2 fail back to back. The first lasted 3 months, a couple thousand miles, the 2nd lasted 5 weeks, also a couple thousand miles. Left me stranded. 275 degree spike followed by coolant puking.

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.