All, thanks for your responses.... The manufactur specs on the in-line thermostat specify that the thermostat must attaches to the inlet port of the cooler. This allows the automatic controller to activate the electric fan to maintain the coolent at 180 degrees.

(http://www.derale.com/fanmountedoilcoolers.shtml)

So back to square one is the upper or lower port the output (HOT) side of the trans?

jc