You still don't get it. Pour some boiling water in a coffee cup and measure the temp of the outside of the cup. This test equals what you have been doing under your hood.
I GET IT DUDE ,your theory that is. First of all I do not buy diagnostic tools from harbor freight
the only things I get there is crap made from china that I can beat the hell out of like punches and such that I know I will destroy. One use items . A quality(not made in China crap) infrared gun is a great tool to have in the chest after it has been verified to be accurate. My temp pistol cost me about 70 bucks and the greatest error I have gotten from it has been 2 degrees and that's close enough for me.