Originally Posted by queensfield
The most common coating used in high end electronics is parylene. It is a good insulator (dielectric) to prevent local arcing- other common insulators do not go down conformally and eventually cause local arcing over time as the insulation degrades. Parylene has low vapor pressure but may evaporate over time. Also, if there is a black-colored material underneath the electronics module, where it is bolted and welded, it is most likely a thermal interface. It is normally used if the housing is plastic (a metal housing won't need it). Do you see any degradation of the interface material, if it is present?
The black material seems to be just a cover over the electronics module. I guess it could be a thermal interface but I don't believe it touches anything to transfer heat. It looks good as new. I will take some pictures and post soon. The electronics housing (of the pump) is metal, I don't see much heat sinking design in it. Considering where the pump is located (the electronics housing is in the back of the pump which faces the radiator and is only about 4 inches away from it), there is not much opportunity for cooling. And to make matters worse the pump is on the exhuast side of the engine close to the exhaust/catalytic converter manifold.