The only thing with this is Aeromotive doesn't recommend a pump that large for the basic 415hp engine. All you're doing is bypassing more fuel, giving it more chance to heat up. If it's going back to the tank is this an issue? Probably not, but I'm going to try the 11109 per their 'power planner' first.

I'd like to try just the return line reroute first, but I'm showing 31psi at cruise and I think that's way lean. Thoughts?

Silent, thanks for starting this thread.

I agree, the proper size pump would be better.

Do u have a VST? So you are going to route the return line that goes back to the VST to the tank?

Ok, so my Baja 38 was upgraded to 2001 502 MPI's with the Cool Fuel under the engine mount. So do I expect problems with these?
Or was it just pre 1999?

I'm going the return line route. Adding another pump, (or 2 in my case) seems to be just 2 more items to go out. K.I.S.S. Not much to go wrong with a rubber hose. So simple even a caveman can do it

I think it's hit or miss.. I've had a 312 with 502 mag MPI's with the cool fuel and never had an issue.. I know some with the exact boat and they vapor lock every time. That's the oddity these were the same boat. My 312 now wit the VST still vapor locks even with the return line,, just not as much anymore... I want the 100% fix I'm done screwing with it.

I definitely get your concern on by-passing this fuel but your always drawing from the cooler fuel at the bottom of the tank. I don't think you'll gain that much heat in the by- pass process.. Theory here only. I did the return thing.. And it worked some.. On mine I think the vapor lock is occurring down by the mechanical pump. Thus when I start my boat it usually runs for about 50 sec. or so then dies. At this point the vapor separator tank is empty and my fuel pressure gage on the rail is at 0. There's nothing to bypass if your not getting any fuel into the VST.. I'm wondering if the vapor-lock is occurring down at the mechanical pump. Besides this with those mechanical pumps they can leak and contaminate the oil for your water pump, or your water pump can leak oil destroying the armature of the fuel pump.. Been there done those too...
Good thing is we are all trying something let's report our endeavors and see how things work..
Merc. Should be paying us

Ok, I will just wait and if I have a problem, just kick the guy laughing or looking strange at me on the dock.....

I currently have a vst and the parts to replace it. Now if I could only find the motivation...

Yes, the return will go back to the tank.

Cool fuel 502mpi's will still vapor lock. Mine are 2000's. They vapor lock rather easily with E10 fuel, but rarely with non ethanol fuel.

Nothing but Non ethanol 93 in it so far. I will keep it that way if I ever get done with it. lol