For many cars of the 1930's and 40's that have grille
louvers that are operated by a shutter thermostat.
This brass shutter thermostat works on many Packards, Cadillacs, Dusenbergs, Chryslers and Pierce Arrows. Works on other cars too.
This vintage car shutter thermostat is made of all brass.
The thermostat will start to open around 148-153 Deg F.
At 170 Deg F. You should be at full stroke.