I never saw any Jeep pumps with plastic veins. Fords are notorious for the veins rusting away.. But I think it is the caliber of owner Fords have... Using the 1/2 by 1/2 water and coolant mixture should cause the pump veins to last the life of the bearings in the pump.
What is the temperature outside when you are testing the temp of the top hose? If it is really cold and the engine isn't toiling, I would suspect the top hose to be cool at worst..
Big JIm

professional bovine relocation specialist