Do thermostats have a break in period?

[ubtripn]

So I have always been fighting finding temp equilibrium on my 68. Standard 350 crate with a new 4 row radiator, new clutch fan and shroud. I just finally decided to run a 165 to keep from cooking her. I now have a new carb and some other parts so I switched to a 180 t-stat. Here is what it does:

Cold start - temp goes to 200 exactly (Mechanical gauge, laser verified) then drops immediately to 180. After I start driving in a normal way, 45 degrees out the temp moves between 180 and 190. Slowly but enough to watch it do it within a few minutes.

I installed it yesterday, it has a 16 pound rad cap. I started it this afternoon, 50 degrees out, it went to 200, dropped to 180 then cycled between 180 and 190 as before. Took it for a short 4 mile drive, parked it and the temp landed on 188 and stayed put. Yesterday it was moving between 180 and 190 in 15 seconds parked with no load. Now it seems to have an equilibrium once it does it a couple times.

1. Do t-stats break in over the first few runs?

2. Is it ok for my radiator to spit a little fluid at 188? If I put a reservoir in would it suck that fluid back in?

It is a good NAPA stat tested before installed, thanks for any help you can provide.