I want to get a new thermostat being i'm changing the valley pan gasket. What does everyone use in their 
car 170 or 180 or what temp is best? I have a 56 Thunderbird with a 312 engine.

Engine wear is reduced and fuel efficiency is improved when using the hotter temperature thermostats.  My own preference is to run 190°/195° thermostats in the daily driver stuff.  I don’t have a problem with an engine running consistently at 210° if I’m not losing any coolant as a result.  On the older cars, the larger radiator tanks do tend to be a problem which may limit the cap pressure you can run which in turn may force the use of a lower temperature rated thermostat.

Lorena, Texas (South of Waco)

While you've got it apart, you might run a search "bypass"., and take a look at the articles. Both the bypass hose and high flow thermostats. Draw your own conclusions, opinion vary. Overheating in 'birds is a common problem in traffic, and occasionally even at speed.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ