correct operating temp 81 351 ford

[coeperc]

Maybe a stupid question, but what would be the 'correct' operating temperature for an 81 351 ford commander.  I just replaced the thermostat with a 160 degree thermostat.  My old one was stuck open and the engine was only getting up to a little over 100 degrees even at 36mph.  With the new thermostat it is running at just under 180 degrees at idle and a little over 160 at higher rpms.  Normal?

Thanks,
Matt

[RonT]

The OEM t-stat is a 143 deg. unit, most use a 160 or a 180 but never higher than 180. What you are describing is perfectly normal, they will fluctuate  more in cold lakes than warmer ones.