Background:
I bought my 2008 Formula 350 Sun Sport last September. Unfortunately during the purchase I made the mistake of asking the broker (an authorized Formula dealer) about the generator operation. With the boat on the trailer my sales lady started the generator (Kohler 7.3ECD) and then couldn't figure out how to shut it off (to be fair it turned out Formula/Kohler has changed the way it is shut off). My hauler luckily knew how to shut it off manually and ran to the back to do so, but anyone with one of these generators or its variants know how tiny and susceptible the impeller is. I unfortunately didn't know and took her word that "it will probably be fine"... it wasn't.

Fast forward to de-winterizing this spring:
I tried running the gen and it shut off after about 30 seconds with the error that it wasn't getting water. Sure enough the impeller was completely toast, only the spindle remained. I found most of the pieces of impeller in the housing and in the edge of the tube and thought I would be fine with the new impeller, NOPE! After disconnecting the water path in multiple places I narrowed it down to the exhaust manifold, and looking at the diagram for it I can understand why - the path splits into like 6 channels that come out around the engine exhaust hole to cool the muffler, it seems this is where the problem is.

The plan:
I bought some 1/2" hose that I plan to hook to the top hose barb that feeds into the exhaust manifold, then hook my shop-vac to that (with the help of some duct tape), then use something narrow to push anything back from the holes on the exhaust side. I have not removed the exhaust pipe yet so I'm not sure if this will be as simple as I envision. Also, is there anywhere else there could likely be bits of impeller? I ran it briefly with the top hose disconnected and the amount of water that came out of the hose was pretty immense, it sure didn't seem like it was being hindered anywhere else.

The Bonus plan:
This design is really annoying, I know I'll have another impeller go out at some point (I already have a spare). When that happens this same problem will occur, and if I'm staying out on the water when it happens then I'm screwed. To remedy this I bought a small seawater strainer that I'm going to put after the impeller housing, this way when it happens again all the impeller bits will get trapped in this strainer and can be easily cleaned out. It's a really small strainer, but anything picked up from the water should be caught in my first (large Perko) strainer, so I expect this one to not accumulate anything unless an impeller fails. Is there any reason this would be a bad idea? It's above the water line so I don't have to worry about flooding if it fails.

Am I asking about this in the wrong place? I figured I would get at least a few comments...

As long as it doesnt choke the water flow down I see no reason why the 2nd strainer would hurt. Since you are installing it just to catch impellor blades, it should have a pretty open screen.

I always backflush coolers when looking for missing impellor blades. Id think that will move lose pieces more so than a shop vac

I agree. And I would plumb/mount it higher as well, so you can bleed air out of the line by opening the second strainer if you ever get an air lock in the system.

How do I backflush when the blockage is in the exhaust manifold exit? I would have to have a way to plumb water into the surrounding 8 holes and not the large center hole where the exhaust gasses come out. I will admit that I'm surprised that this is the only place blocking flow and it is 100% blocked (or very close to it). I have attached a diagram that shows the part that is blocked, from my understanding the path is simply the 1/2" barb to the 8 small diameter holes where it combines with the the exhaust gas and cools the metal exhaust pipe.



Top and side view of exhaust manifold

It's not very big but it can handle 150PSI, I doubt the tiny impeller is putting out that much.

I probably won't be mounting it up high because that would require a lot more tubing and work. I'm not sure how an air bubble would be a problem when it's past the pump, the water is under positive pressure at that point, not negative so it should either push through the system. In fact, I expect there is plenty of air in the system when the generator isn't running (since the stopped impeller doesn't create a watertight seal), the water in the system should normalize at the water line.

Hmmm, cant help on the ex manifold. Going to be challenge. Does that end cap come off? Your plan sounds like a place to start, and see what happens.

Is the 1/2" strainer big enough? My gen uses 3/4" hoses. Pressure isn't the concern, but volume. Just thinking that the 1/2" barbs, though they except 1/2" ID hose, the barb itself is smaller yet. Just something to ponder. Good luck

Update:
The good news - THE GENERATOR IS WORKING!!!
The bad news - It wasn't impeller pieces clogging it, it was... SALT!

This really pissed me off since the boat was serviced by Formula AND had gone through a survey where both apparently tested the generator, but from what I saw when I got the exhaust off, there's just no way there was water getting through this even remotely recently. I think they ran it long enough to say it runs, but turned it off before it shut down due to lack of coolant. I'll get the pics posted shortly, the manifold/exhaust doesn't exactly match what the diagram shows, instead it has 4 quarter-circle shaped holes... or at least it should have. I had to dig through like 1/2" of salt on the manifold side!

The ugly: During exhaust removal I snapped a bolt off in the manifold and I don't think I can easily drill it out because of access challenges. I have a good 1" C-clamp on there right now that may just become a permanent solution since nobody will ever see it. Ghetto, I know.
The dumb: I thought I knew the tube diameter, but I was wrong,,, turns out it was 5/8", not 1/2", so my tubing and strainer couldn't even be installed.

Let's play a game of "find the holes" (no, not the fun version played with females)


Can't find them? Here's the exhaust to use as a slightly better guide:


Sorry, I don't have an after pic. I used a drill bit (by hand) to clear the holes and then my Ryobi multitool with sanding pad to polish up both faces to a smooth finish. The gaskets weren't nearly as bad as they look in this picture and have been reused, at least for now. Even before adding the clamp (only 3 bolts) it didn't leak at all.

Glad you got it figured out. I would run some Salt Away through the generator. It probably has some build up in other places.

Dont know anything about your generator but large boats that have heat exchangers, on motors and generators usually have Barnicle Buster chemical treatment done every 3 years or so. Involves taking apart where raw water enters the system and and pumping the solvent through there and capturing the solvent in a bucket or tube attached to the exit going to a bucket. Fluid/solvent is pumped from the bucket and back into the raw water intake. Its a closed circulation system for 4 to 8 hours.

Chris