Would increasing the fittings on the radiator where the tranny fluid is cooled, from 5/16 npt to 1/2 npt have any adverse effect on the tranny?

Is increased flow a bad thing, in the winter for example?

 

But increasing the fitting dia. without increasing line size isn't going to increase any fluid flow.

 

What are you exactly trying to accomplish? Have you thought about getting an aftermarket tranny cooler?

 

I have a b&m 70266 cooler and am trying to find the fittings for it to match the one's coming out of the radiator cooler. Those are 5/16, but I am not sure if that's the barb or the thread of the nipple/fitting.

 

I see. Just match the hose size to the OEM fittings first.