The check valve may be a safety of sorts in the event of a failed
thermostat in the closed mode. Sounds to me like it is made to bleed if
that is the case.

Just guessing.

Regards,

John Rodgers
88 GL Driver

]John Graham wrote:

>Over the weekend I changed out my thermostat as it just wasn't warming
>up very well in cold weather.  The temp guage needle would seldom
>reach the mid point of the scale where it normally rides.
>
>When I removed the old thermostat, I realized that it had a little
>checkvalve feature on the outer ring - sorta like a little BB in a
>cage.  The old thermostat had official VW and Audi stamps on it and a
>part number of 078 121 113F.  I would guess that the mini checkvalve
>might have something to do with allowing air to escape the lower parts
>of the engine etc.  Just guessing
>
>The new thermostat didn't have this checkvalve feature and had a part
>number of 025 121 113F.  The box says it's made by Behr.  Both
>thermostats were obtained from a reputable online vendor though
>several years apart.  The new thermostat does seem to work better in
>keeping the engine temp up in the middle of the range, which is what I
>was after.  I'm just curious as to whether it matters whether or not
>my thermostat has this little check valve
>
>Whatcha know?
>
>John Graham
>88 Westy
>Charlotte NC
>
>
>
>