Mercruiser 350 MAG MPI Water Leaking

[aboston7]

Hello,

I have water leaking on spark plugs of my Mercruiser 350 MAG MPI (on the starboard of the motor).

I've checked the manifold, risers and extensions and they look good. Not sure what else it could be. It seems that it's leaking on the 3rd spark plug from somewhere...

Any ideas? Thank you in advance!

 

[Espos4]

Do you mean that water is leaking onto the portion of the spark plug that is visible, where the spark plug wire attaches?

Or is there water inside the cylinder that comes out when you remove the spark plug?

 

[aboston7]

Correct, I can see water leaking from the spark plug wires, but not from the spark plugs themselves. I removed the sparkplugs and there is no water in the cylinders which is good, but I'm still puzzled.

 

[Espos4]

There is a water hose and 90° Swivel fitting attached to the underside of the exhaust manifold in that area. Maybe a broken clamp or the swivel is leaking.

How old are the manifolds and risers?

With salt water use, they rust from the inside out and eventually get clogged. That can trap water and cause a hairline crack over the winter.

I had that issue a few years back. The port side manifold had a hairline crack above the center exhaust ports.
I was seeing an occasional wisp of steam as the salt water leaked out and was boiled off as it hit the hot exhaust port.

Take a look around, especially under/behind the ECM mounted on the riser.