Over heated Ford (Mercury) Engine on my F8

[Phil Waterman]

Question for you are the thermostats new? Did you test them to be sure they are actually opening at the rated temperature? I've been doing test on all the thermostats I've put in rebuilding engines last couple of years and discovered a interesting thing. Brand new fresh from the manufacture thermostats are often slow opening the first dozen or so times they open and close. Which will cause and engine to run hot the first few times you bring it up to temperature. There is a big difference in how fast heats the engine pushing the truck down the road than running the engine stationary.

What I do now with new or even old thermostats I test them and cycle them on the stove in a pot of water. Bring the water up to the rated temp 140 180 what ever then dip (using tongs) the thermostat in see how quick in opens. Then dip it into cold water. Do this several times you will be surprised that with a new thermostat it will open a little faster each time.