Thanks for you advice. I went out an purchased an infrared thermometer with an adjustable emissivity feature. I then contacted the manufacturer of my aluminum radiator to find the grade of aluminum that their radiator was constructed with. They replied that it was 4043 rough aluminum. At that point I began to Google emissivity ratings for the above mentioned. Not knowing enough about what this would translate to I am seeing ratings for oxidized aluminum, polished, plain sheet etc., but nothing that I can understand would pertain to my radiator. Any suggestions on where else I might look to for a more definite answer? Thanks again for the advice, I learned quite a bit about the importance of knowing what I am pointing that device at.