Hi all , my stock 75 L48 is running cool and when I bring it to operating temperature it’s  (165) ..all of my insulation around radiator is correct, and I installed a new thermostat (180) and still running cool . I also put thermal gun on and this is what I got . I did plug up vacuum hose to heat riser would that effect it ? Any help would be appreciated thanks

upper rad hose -165                          

Thermostat housing-165

lower rad hose-120

upper neck on rad -180 

I 

I once read where the thermostat tolerance was +/- 20%.

You can check the tolerance of your temperature gun by pointing it at the side of a saucepan that contains boiling water.

Out of curiosity, what is your instrument panel temperature gauge say?

Right at 160

If your temp gun proves to be accurate, then I'd try another t-stat.

Maybe a 195

Is that the temps you see while driving it, or just sitting? Can't say I've ever heard of a '68-'82 car running too cool....😮 Changing the t-stat opening temp will only change the temp that the stat opens to allow full coolant flow. Once open, the t-stat no longer has any real control over engine temp. Engine temp(after stat opening) is mostly controlled by coolant flow thru the radiator(water pump), and air flow thru the radiator(fan). Another often overlooked contributor to engine temp is ignition timing. Severely retarded timing will cause high cylinder temps, as will extreme advanced timing. If it is actually running 160 deg while driving, I would add a few degrees of timing.....it'll prolly run a little better too.

What are the ambient temps when you are checking the coolant temps?

A car thermostat does control the engine coolant temperature. It opens and closes to regulate the temperature within a tolerance band of the temperature on the thermostat. It's just like the thermostat in your house where it controls the temperature set on it.

The radiator's function is to remove heat from the coolant. And the water pump then circulates the coolant to the degree that the thermostat allows it to. In the winter time the thermostat will just barely open to maintain the required temperature of the coolant in the engine block.

I had a thermostat that I found to be stuck open about 1/16" and the car would never get warm in the winter time.

The outside temp was about 50 in New York however was running cool in warmer temps as well 

Driving also 160-165 

Ok possibly a defective stat I’ll try a new one and keep you updated  thank you 73 shark