Thermostat OEM Volkswagen or OEM Mazda

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.

Always buy the Mazda OEM branded thermostat from any local or online Mazda factory parts retailer, this is not the item you want to save a couple bucks on, no matter how much you trust that ‘other’ brand.

Make sure you use a Mazda OEM thermostat. I wouldn’t trust anything but OEM for those.

Noticed coolant was low and could smell it sometimes. Dealership pressure tested system and found coolant leak at thermostat housing. Thermostat replaced under warranty. Its probably been leaking slowly for a year or more.

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

Thermostat failed multiple times

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 just had the code P0126 on my 2021 mazda cx-30 with 20,000 miles. Seems to be the same issue