http://www.harborfreight.com/non-contact-laser-thermometer-96451.html



$39.99.

Sure, there may be better units out there but what you're looking for is a noticeable change in temperature.

When my Imperial had a clogged radiator there were areas where the temperature dropped almost 50 degrees lower than surrounding bits of the radiator.

We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind.
- Stu Harmon