Thermostat Wahler or OEM Volkswagen

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.

Replaced the new Mahle/Behr one with a new Wahler one, and now it runs at 97° under low load and 80° under high load, as it should, and seems to be fine.

I replaced the thermostat myself. It’s in a pretty bad place, hidden under the intake manifold. It took me about 3 hours to get the job done, had to use a mirror to see the screws. Mine was stuck open so the car in winter time wouldn’t even reach 190 F. I bought an OEM Wahler 07K121113B thermostat from Amazon for like 30$, so far has been working great.

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.

Independent mechanic noticed leak. Dealership confirmed the thermostat was cracked and leaking. Took a week for parts to arrive. Took a day to repair. All covered under warranty.

Bypass thermostat yellow arrow Included with radiator upper hose and you should be able to find the bypass by itself.

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.

Thermostat was ALSO replaced when the water pump was, with a Wahler unit. Guess I got 10k miles out of it?

I had two Wahlers and they leaked as soon as I fitted them. In exactly the way you described.

I got the wahler one in 2019, that would explain the really slow leak I have.