I have noticed a trend, itself the result of Internet generated over-thinking. That is, majoring in the minors, focusing on the trivial while ignoring the important. This kind of thinking is endemic online, it's what "armchair" mechanics do. What else is there to do in front of a personal computer late at night?

This trend, as I say, is the attempt to use infrared temperature guns in engine diagnosis. It's silly. There is no good reason to think that each cylinder in an engine should be exactly the same temperature. That would be surprising, actually. The mass-produced, passenger vehicle, internal combustion engine has hardly changed for more than a hundred years. It's an extremely crude device. It's a machine. It's not a space shuttle. It is not built for fuel economy; it is not built for efficiency of any kind. It is built to last X number of miles when given X amount of attention for X amount of dollars. It is made to haul a carcass, that is all. It is built to make money.

Why career mechanics understand this intuitively and everyone else does not is a mystery. Like so much of the disparity between forums and the real world. A dichotomy. A disconnect. There are of course great diagnostic and tuning tools available. EGAs, leakdown testers, compression testers, dynos, onboard oxygen sensors, ignition oscilloscopes, and more. And I have used them all. But a heat gun, which encourages folks to get all worked up over a 20 degree difference, isn't one of them.