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