First, thermostats did not start until 1928 on Chevrolet.
Second,ignition timing can have a lot to do with overheating.
I recently worked on a 1926 where everything checked out but overheated. I found there to be 2" of rust in the bottom of the engine water jacket. After cleaning that out the overheating problem went away.


See the USA in your vintage Chevrolet!
My Blog