I just installed a new stewart pump on my 383. I am running a 180 degree thermostat. With the old waterpump, my engine temps stayed right at 180 degrees, which is good. Now with the stewart pump the temp is not staying hot enough to run at 180. The temp is now staying right around 165-170 degrees, hince thermostat is not staying open. The temp will reach 180, but then automatically shoots back down to 165-170. This is a continuous process while operating my 68 chevelle. Do I need to go to a 160 degree thermostat or a 195 degree one??
Any advice would be greatly appreciated.....

If you want it to run hotter put the 195 one in it. Putting a 160 in it will make it stay in the same range you have now.

If you want it to run hotter put the 195 one in it. Putting a 160 in it will make it stay in the same range you have now.

Yes I want it to run hotter, so the thermostat will stay open under normal operation. Does that make sense???

Like I said, 195 :beers:

Like I said, 195 :beers:

I hope you know I was not doubting your knowledge, if I was I would tell you... LOL!!!!!!

This is what we control engineers call "limit cycling" or an "underdamped system". The engine heat, radiator, fan, water, water pump and thermostat form a feebdack control system. The stat opens quickly as the water nears temp, then the rad cools it off quickly, so the temp undershoots the set point. This causes the stat to close again as the water heats up, stat opens and the cycle repeats itself.

You will need to drill 1 or 2 small holes in the thermostat to provide "damping".

Once warmed up, there's no way coolant will be lower than a properly functioning thermostat's set-point.

I hope you know I was not doubting your knowledge, if I was I would tell you... LOL!!!!!!
I guess you didn't realize I'm omniscient also ;)