I have a 496 Mag HO with a closed coolant system, with steam coming out of the port side (I believe, hard to tell with the swim platform). I pulled the riser off and found no water in the manifold, put it back together and the steam was worse. So I figure thats were it is leaking. On my way back across the lake it started missing. My question is, could it have gotten the plug or plugs wet enough to foul them? I pulled the plugs and the back two looked black. No water in the cylinder or the oil. Thanks for your time and help!!

Sounds to me like its running rich on the rear corner !!??

Maybe injectors or sensors ?

What year is your 496 and how many hours on the engine??

Best Regards,
Ray @ Raylar

It has less than 4 hours, just rebuilt it, didn't change out the riser manifold gaskets. Is it possible that water got into the cylinder, and fouled the plug or plugs from the gaskets leaking?

It has less than 4 hours, just rebuilt it, didn't change out the riser manifold gaskets. Is it possible that water got into the cylinder, and fouled the plug or plugs from the gaskets leaking?