OK, here's an easy one, maybe. New rebuilt engine going back together, 265 4 BBL PowerPak Powerglide. Can't find a reference for what temp T-stat is "standard." I find in the 1955 Shop Manual it says "thermostat starts opening at 157-163, fully open at 180" or something to that effect. Can't decide if that means a 160 or a 180..... Nothing in Assembly Manual or Owners Manual.

1954's and up came from the factory with a 170 degree thermostat. The 170 has not been made for many years. What is available is a 160 and a 180. I have always run a 160 in my cars as they are not driven in winter.

I agree with Gene. I too would recommend running a 160 degree thermostat as well.

Well, Skipper, Gene beat you by 4 minutes this time (and I saw both replies this time, too). So - thank you Gene and Skipper - and with that unanimous early opinion, a 160 it shall be. I like that answer. It had a 180 in it when I pulled it apart. Odd that they don't talk about it in any of the manuals.

All internal engines run best at 180 deg. The newer engines run hotter because of pollution stuff and maybe the E10 gas, I don't know.

In 100 years you will never tell the difference if the engine is running at 160 or 180 degrees + in the summer time they often run at over 160 Deg. anyway.
The 180 is better in cold weather for heater heat and the oil may run a little hotter to boil off the gas and water in it.
I guess it is all up to what you feel comfortable with.
When I flush my '57 this year I am going to install a 180 and see what happens.

Aught, oh - is this wavering I detect on the 160 recommendation???

From past experience, I would stay with a 160 degree thermostat.

For a car that you have had no driving experiance with and a fresh tight engine I would start with a 160.
My 1957 has a rather new aftermarket replacement radiator and I have driven it many thousands of miles with the original and new radiator.
It never took much to get the temperature gauge to run on the high side, either in 90 Deg. weather on the highway or in a parade. Last year I removed the fine mesh bug screen from in front of the radiator that had been there for years. After that the temp. stayed in the 160 Deg. range almost all the time.
The actual genuine Chevrolet bug screens like I have on my 1950 has a real coarse mesh and never caused a problem.
The moral of the story is do not use a bug screen that has fine mesh like a window screen.

I base this on books I read during my racing days and some of it was information from dyno tests.

I understand. I have read the same thing but feel it does not pertain to 70 year old cars with 70 year old parts.

Actual experience is the best teacher. Some of my vehicles used to run hot when driving. I removed the 180 degree "stat" and went with the 160 "stat" and that made a major difference on the cooling capabilities. Those vehicles now run at normal temperature on a 100 degree day.