Old_School_Audi

Audi began using a Nylon 66 glass filled (plastic) thermostat housings in 2001. These are now up to 13 yrs old. Owners are discovering the problems when these warp and crack. Some of the plastic housings leak right after replacing the thermosat due to warping. Labor cost to replace can be over $200. The fix is to replace with the more expensive but reliable pre-2001 aluminum factory part shown here during the timing belt service.

Comes with a new thermostat O-ring. Compare this to new at $130+ for aftermarket. This is an OEM part.
078-121-121J
078 121 121 J
078121121J

Located in Kansas City
Contact Chris here - --e-mail LINK--

Link to repair article

Link to forum post on housing part numbers