Increased cooling for headers question
 

I'm running a Mercury 525efi with Hurricane lite headers in a Fountain sportfish with stepped hull. Headers keep getting too hot when I run hard. They just aren't getting enough water with my current setup. I'm running a dual pickup Bravo XR lower. When I get the boat trimmed up where it likes to run, I get too many bubbles and the water pressure jumps up and down on the gauge in unison with hitting waves. This is what I'm thinking about doing:
Close off the side inlets on the drive.
Add a transom mounted water pickup.
Plumb the water from the current drive hose and the transom pickup water into a sea strainer with two inlets and one outlet.
Install a two stage water pump that pulls from the sea strainer.
Has anyone tried this setup? I've replaced my water pump and checked every inch of my cooling system for corrosion, blockages or kinks in hoses. Everything is completely clean and clear.

Have you eliminated the hose that runs between the back of the header water supply to the tailpipe? This thread might help:

https://www.offshoreonly.com/forums/...tail-pipe.html

Yep I removed it when I went from the stock CMI headers to the Hurricanes last year. I've also tried it with restrictors in and removed. I was scratching my head until I hooked up a clear hose to the port side header. As soon as I trim up a little bit it turns white almost like there's foam in the lines. My theory is that the side inlets on the drive are not getting good suction and are sucking air in.

Duplicate post

Try plugging the top 2 holes on the side inlets with 1/6 brass pipe plugs. Or else you plan sounds good but possibly not needed.

Have you checked drive for corrosion where hose connects?


https://cimg6.ibsrv.net/gimg/www.off...b8ec5e2ac.jpeg

I forgot completely about that!!

I haven't pulled the lower but when I back flush there's no restriction at all. It's worth a look though. Would that create bubbles in the system? It seems to cool ok at slower speeds.

How far up are you trimming ? where is the prop shaft in relation to the bottom of the hull

not at the lower. It’s where tube is plumbed from sea strainer to outdrive in bilge. On the transom assembly

Oh gotcha. I'll check it this weekend. We usually trim it just up until the boat is running the most mph with no tabs and then bring it back down a touch. I'm not trimming it way up at all. Usually about +2 on the gauge. Usually cruise at 45-50 mph. I'm not currently running a sea strainer but definitely installing one before this season. If running a transom pickup into the second input for the strainer won't mess with anything I think I will do it for insurance. I make a lot of 30 plus mile runs at a time fishing offshore. I don't want to constantly be worrying about water getting to the headers. I don't have any issues at all with motor temps but keep discoloring the headers.

My engine guy told me on my old setup that I was blowing water out of the top of the side vents and I should plug the top 2-3 holes. It was fine at cruise. I never ran hard for very long so I let it be but if you are then it's a cheap fix to try

Anyone got a picture that shows how you plug the top few holes on the side inlets? I checked everything yesterday and there's no corrosion at all so I'm back to trying to eliminate it from sucking air from the side inlets.

Do you mean you pulled the water fitting as shown in the photo? That can be a real pita to get off. No other way to check it.

There is a service bulletin re the holes. I'll see if I can find it.

It just involves a tap and some pipe plugs.

I cheated. It's really hard to get to with the headers on so I disconnected the hose at the valve and ran a camera down it. There's no blockages or corrosion to be seen at all.