Tom M'Guinn

The radiator is plastic and aluminum - bone stock. The sensor is plastic and what appears to be brass. THe green corrossion is only present on the brass part of the sensor.

z3bra

Alright, just couldn't tell exactly what it was from the picture, don't worry about it then, maybe teflon tape the threads or something if you want. It's just the seepage reacting with the brass on your sensor. Sorry for all the commotion there, I was thinking in old car mode.