Omc cobra 3.0 overheating

[Ole walk walk]

I've replaced the impeller, and the thermostat. I've also cleaned all the rust and debris out of the thermostat housing. Boat ran fine after I did all that. All the sudden I'm out on the lake and it over heats. Checked impeller out and its fine. Noticed water leaking into the bilge area from somewhere. Also notice a little water on top of the engine where the water manifold bolts to the block. It bubbles there. What should I do? What else should I check.

 

[94fwfreedom]

Re: Omc cobra 3.0 overheating

The passage between the manifold and the riser is very narrow, and can easily get blocked with rust which can get loosened up inside the engine. If you already have noticed corrosion on the thermostat, then it is likely that some chunks came loose and lodged into those passages. The quick fix is to remove the exhaust riser (also known as elbow) and have a look. My v6 omc motor did exactly the same, ran perfect on the hose, but when I ran it on the lake all the rust worked loose and clogged the holes.

Another issue could be the exhaust flapper right below the elbow. It is made of plastic and can melt off its rod, fall down into the exhaust tub, and lodge itself into the outdrive exhaust bellows. That is where I found my burned flapper, once I removed the outdrive!!

The attached image is a mercruiser manifold, but shows the small passages. After cleaning (screwdriver, etc, and shop vac.), you will need to order the correct manifold riser gasket. I found mine here, it was $10.

 

[Ole walk walk]

Re: Omc cobra 3.0 overheating

OK, thanks that's what I was thinking but wanted to get a second opinion. That would fix the over heating issue. How do I explain the leaking between the exhaust manifold and the head? Just a blown gasket im guessing? Ive also read on here there is a trick to pulling the exhaust manifold me?? Looks simple to me. Are there any torque specs when I put it back on after I pull it? Any tricks? Thanks for your help.

 

[94fwfreedom]

Re: Omc cobra 3.0 overheating

The leaking must be caused by pressure built up of the cooling water not being able to exit. But it may also indicate deeper trouble, such as a cracked manifold. Don S has a write up on testing the manifold for an internal crack using acetone.
I do not have a manual, removal is straight forward, and once again, Don has a write up posted under adults only off a omc dealer service bulletin on removal, inspection and re installation of the manifolds.

Good luck. Btw, I had squirrels living in my exhaust!!