I've done the same temp testing with an immersed TC and my Fluke 52. My D80 on a 97 CTD ran up to 285* and the Mag hytec cover only cooled it 3*. Blasting down the road at 75 mph ran hotter than pulling up to Eisenhower tunnel... so speed was worse than load for heat. I like the looks of the deep fins, for effectiveness, on my AAM max tow cover. The after market covers are a waste of money IMO. Craig