Originally Posted by dieseldiehard

I am now testing Viton hose as return lines on a 603 engine. So far it is holding up very well. I will post results about a year from now as to their longevity. I believe Viton will significantly outlast the OE hose material. The reason the material deteriorates so fast (18 months is about all it is good for) is because the fuel is really hot coming off the injectors and hot fuel aggressively attacks the OE rubber and it gets soft and fuel weeps thru.