i just recently put a new(rebuilt crate engine) in my 86 f150 with a 4.9 it has a new quad core raditator in it a new water pump and a new thermostat but im going to change it to a lower temp thermostat soon. the time is set to 6 degrees. when im driving the truck the temp shoots up suddenly. the gauge has normal in between the c and the h , the needle hovers around the a in normal and makes me very nervous.

 

Depending on where you reside , a 195 thermostat will provide better heat and the engine will run more efficiently. Something else to check, compare the water pump impellers to confirm they are the same type, make sure there is a spring in the lower hose to prevent it from collapsing with higher engine RPM and restricting coolant flow, last if the belt is installed where it causes the water pump to turn in the wrong direction make sure that is correct. (Don;t remember if that engine has a serp belt)

Some engines did run with the temp needle there !