370DA fuel line sizes

Question for the smart engine and manufacturer guys...

My fuel line circuit is as follows:
Tank to fuel shutoff solenoid 5/8" pickup and hose steps down to
fuel shutoff solenoid 3/8" inlet
shutoff solenoid 3/8" outlet steps up to 5/8"hose and then steps down to
fuel water separator 3/8" inlet and 3/8" pipe outlet to fuel cooler and pump.

So the question is what's the significance of using 5/8" hose? Is it a cost savings issue (same hose for many boats) or is there a reason to have larger sizes inline with all the 3/8" fittings inline?

Not sure why the up/down assembly. All mine are 3/8".

370Dancer said:

Question for the smart engine and manufacturer guys...

My fuel line circuit is as follows:
Tank to fuel shutoff solenoid 5/8" pickup and hose steps down to
fuel shutoff solenoid 3/8" inlet
shutoff solenoid 3/8" outlet steps up to 5/8"hose and then steps down to
fuel water separator 3/8" inlet and 3/8" pipe outlet to fuel cooler and pump.

So the question is what's the significance of using 5/8" hose? Is it a cost savings issue (same hose for many boats) or is there a reason to have larger sizes inline with all the 3/8" fittings inline?

Click to expand...

Yup, it's 7 years later, and I still don't have a good answer for this. I'm thinking that perhaps the P.O. was experiencing vapor lock, and the dealership recommended increasing the fuel line size. Before I conclude that, though, maybe it's taking into consideration that the engines are 380hp MAG MPI Horizons, and not the base 310HP engines as likely depicted in the 1998 parts manual. In there, everything is 3/8". I have repowered now, with another pair of 380HP MAG MPIs, and will be installing the boost pump kit on each engine to overcome the vapor lock. Since I am replacing all fuel lines from the tank to the fuel water separator, I'd like to do it once, but right. Any other 370 owners have 1/2" lines from the shutoff solenoid to the filter bracket? Referencing the 2002 380 DA parts manual, those fuel lines are 1/2", but still start off at 3/8"at the tank!
Finally, the SAE fittings are nice for quick disconnections. These are usually installed on hydraulic lines with a metal outer band. Still ok to use these on regular A1 fuel line? I am talking about the field installable ones, that wrench together with a mandrel, not the crimp style. My reference is Parker series 233 fittings.