Can a return line be all rubber fuel line or does it have to be steel? 69 cutlass.

 

I'd recommend stainless steel with todays fuels. You may have to use rubber for certain junctions and connections but it should be kept to a minimum. Rubber deteriorates over time and you would need a lot of clamps to keep it from whipping during normal driving.

 

Ok thanks, was just thinking it’d be easier to install and since it’s already rubber on both ends, why not the whole way. Also being a convertible, I could run it in the frame.

 

Rubber deteriorates over time and is more easily damaged by stones kicked up from the tires. The short sections used from the factory are the minimum needed to accommodate assembly and engine motion.