fuel pump overheating

[Will Fish]

I'm purchasing a boat with twin 5.7 Crusader Captains Choice MPI motors with very low hours. Part of the deal was the seller would have crusader go over the motors. It just so happened in the few days from when I looked at the boat and sea trialed to the time crusader got their hands on it, one motor developed an issue. The boat ran great at idle and you could even bring her up to WOT. Once backed down the motor would stutter and stall out, and would not start unless left alone for at least 20 min. Sounds like a fuel problem. Tank cleaned (I doubt this was the issue, as only 1 motor had the problem, but at least I know the tank is clean now), all filters changed despite looking clean and only had about 20 hours on them, pressure tested fuel pumps and checked ok at the dock. When testing pressure under load, the pressure dropped on the HP pump. When touching the strainer she was hot. the other motor which ran fine was cool to the touch. Mechanic said the HP pump is raw water cooled off the riser. Pulled the hose from the riser and sure enough, no water. Cleared the clog in the riser and put back together. Now everything checks out fine.

I have a few concerns:

1. I cannot find a diagram in any of the crusader books showing a raw water hose from the riser to the fuel pump (Motors were done in 2007, but I do not have the serial numbers to confirm the year of the motor)
2. Even if the HP pump is raw water cooled, wouldn't no water damage the pump?
3. Shouldn't the risers be changed? I've never hear of cleaning the riser. When they fail, they usually need to be replaced.

Seems like a simple but PIA to diagnose problem. At the same time, I want to make sure everything checks out before I take delivery.

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[Blue2005]

I can't talk about your engine specifically but on my Volvo, my fuel pump is indeed water cooled, so I'm assuming it's similar to your setup. I have a hose coming from the thermostat housing that feeds water to the pump which then takes the water to the exhaust manifold. When it is clogged or kinked, water doesn't flow out and the pump starts to overheat (I had this happen to me).

Regarding the risers/manifolds, they get changed when they go bad. Never heard of cleaning them. But maybe somebody with more experience could chime in on this.

 

[Will Fish]

He said the riser was clogged and just had to clear the clog???

 

[alldodge]

Finding info on a Crusader is ruff, at least for me. Found a parts manual for the 7.4 carb and owners manual but no much else.

I can see how the boat would run fine and go down hill when slowed down from all the heat on the pump. Probably boiling the gas. Exhaust components replacement in most cases is time and if salt is involved. Fresh water boat will last the motor, salt not so much

 

[Will Fish]

The motor is FWC, including the manifold which I was very impressed with, since I've only had Mercs. Raw water runs thru the heat exchanger, Oil cooler transmission cooler, and the fuel pump (from what I could find), and then dumps thru the risers. The risers are plated off when mated to the manifolds.

I guess it would make sense to vapor lock the fuel with no cooling. Not sure if it would damage the pump with no water? Or if the riser is clogged, its the tell tale sign they need replacement?

 

[alldodge]

The check is look at the slotted holes are see how much erosion has happened. I typical Merc slot is about 1/4 inch, if it gets much wider then that, its time to replace