I have a 1995 225 Mariner Magnum EFI 3.0(I can get serial # if needed, but boat is current shrink wrapped). It has 300 heads, cut can, and 4 hole intake. Other than that it has never been touched except for routine maintenance since 97 when most mods were done.

When I went to winterize it, the mid plug on the left side of the engine was milky. Cylinder 3 or 4? The cylinder was not wet with water, and I spun the motor over with the plug out. So I added some premium plus to the cylinder a spun the motor over a couple times to make sure it was lubed well. I did the same for all the other cylinders as well when I winterized it. All other plugs looked good.

I first suspected the o-ring on the head and plan to replace them, but further research I found it may be the exhaust divider plate, or the base gasket. Any ideas?

Last time I ran the boat on the lake it wasn't missing or anything, but I did notice at idle, some water was spitting out of the above water exhaust relief. The motor had never done that before, but I just replaced the water pump and chalked it up to extra pressure at idle. I don't have any water pressure issues or have in the past, 5-6 psi idle and 12-15 at WOT.

So am I on the right track? Should I replace all o-rings and gaskets, or just start tearing down to find the reason? I have a factory service manual and am comfortable and mechanically inclined enough to do the job, just looking for any extra input before I begin.

Thank you for any advice. (Sorry for the book)

Matt