low engine temp.

The thermostat might be missing, or jammed open?
regards
Mike

thermostat is brand new. just installed

For that model the thermostat should be opening @ 175 deg. and full open @ 186 deg. F.
Minimum operating temperature should be above 160 deg. F.
Is the temperature indicator working correctly?

gauge is working. put sender in pan of water and heated

Hmmm, couple more then I'm done...

Is the thermostat properly seating in it's bore?

A certain amount of water bypasses the thermostat from head to water pump through a bypass line, does this appear corroded so that it has become oversize?

thermostat sits perfect in its bore and bypass hole is as clean as the day it was made

Do you know the history of the radiator core?....maybe replaced with a higher capacity heat transfer unit?

When you tested the gauge you took the water all the way to boil?Had a gauge that worked in the lower temperature range but stopped before the red.Had never seen one that worked at all that wouldn't read the whole range before this one.
If you don't us it a lot just us card board to block air flow to get the desired temperature.Good luck.
Ray

There is no way I would start trying to push up the temperature without knowing what it actually is, it could be at the correct temperature, gte hold of a thermometer or graduated gauge and check it out properly. There is probably nothing wrong.