One way to see where the heat is building up is to use one of those infra-red point and shoot thermometer. If everything is working right, you should see everything working well, and normal drops, etc...

But if lets say the thermostat isn't working, or the radiator is plugged or something in the engine, you should be able to see where the issue is because it will be really hot on one side, and much cooler on the other.

Feets did this on Power Tour for a friend and discovered that his brand new thermostat had gone bad.

Ryan