This factoid might save you a return trip to the parts store:
Advance Auto Parts lists the wrong thermostats for Buick 215. (Incidentally NAPA lists the wrong ones too.)
The ones they list have 63mm diameter flanges. Our classic aluminum V8s require 54mm diameter flanges.
As so often happens, you can get to the correct parts by looking up a 1980 Buick 3.8L V6... Advance lists multiple different thermostat options: nominally "good", "better", and "best" and also various heat ratings. I was there to get a 180 degree thermostat to install in place of a 160 degree stat I've used for years.
I chose Stant "Superstat" part number 45358 - which was the "best" quality, 180 degree F, 54mm option. Price: $7.99
Incidentally, "USA" is stamped into the body of part number 45358. However, the wrong-size Superstat they sold me last night (part# 45478) was NOT marked USA. Its box said "Engineered in USA". I believe that's often code for Made-in-China. Also incidentally, I tested 45358 in a saucepan of water on my kitchen stove. At ~180 degrees it opened ~1/8". By 190 it was open ~3/8".
They are all wrong, Curtis. No stinkin' 54mm 'stat for my 215. ;) I just bought one for an old Camaro. It was a 2 1/8" Robertshaw high flow with bypass hole. When in doubt ask for Chevy parts. I used to do the same when I ran points.