Rust On The Outside Of Spark Plugs

[thaddeus76]

Hello,
I have a 1986 mercruiser 140.

I have searched for a couple hours on rust on spark plugs. What I've found is that it's an indicator of a bad exhaust manifold and/or Riser, among other things. However, I have not found where this rust has to be on the spark plug to be a problem. Mine is on the outside.

I ran the boat today for the first time since November. After it ran for about 5minutes, I shut it off because my brass drain plug off the exhaust manifold was dripping. It wasn't completely in. When I pulled it off, all the water obviously came out, but I noticed these little black flake sediments. This caught me off guard.

A little while later, I went to check out the spark plugs and found this on 2 of the 4 spark plugs. There is also rust on the outside of the engine where these spark plugs screw into. It's like a bowl and I wondered if moisture was collecting there, causing the rust.

http://picasaweb.google.com/JThadH/S...ey=_2KoIotnjOM


This boat did sit on a trailer all winter, under a boat cover, but the motor box was in the house. The boat cover is not 100% waterproof and the rain would sometimes get in the boat, and periodically, I would pump it out of the bilge.

My internet research on sediment in the exhaust manifold, coupled with the rust on the plugs, is starting to concern me.

My question is: Is this the classic "bad exhaust manifold/blown head gasket/Water getting in the engine" scenario or does the spark side of the plug look normal, and the rust on the outside just coming from being layed up not completely protected?

Thanks. I appreciate your help.

[Mkos1980]

Condensation can cause rust on the spark plugs too. Looks normal to me. Even my MR43T's I used to have on with it being stainless still rusted a little.

[Bond-o]

This boat did sit on a trailer all winter, under a boat cover, but the motor box was in the house. The boat cover is not 100% waterproof and the rain would sometimes get in the boat, and periodically, I would pump it out of the bilge.

Ayuh,.......

Surface rust on the Outside of the plugs is an indicator that they've been Wet,......
Nothing More......
Rust on the Working End of the Sparkplugs indicates water In the motor....

And,........
Why would anybody lay-up a boat with the Bilge Plug left in it,..??..??
If the bow is raised,+ the Bilge Plug is left Out,....
It'll drain All by Itself...... No bilgepump Necessary......

[JustJason]

nothing "wrong" per se with those plugs.
But they are a little sooty... for best performance i'd replace them.

[thaddeus76]

Thanks for all the responses. I was hoping that was the case. I plan on getting new plugs this week and maybe hit it with some silicone to prevent that rusting.

And,........
Why would anybody lay-up a boat with the Bilge Plug left in it,..??..??
If the bow is raised,+ the Bilge Plug is left Out,....
It'll drain All by Itself...... No bilgepump Necessary......

The bilge plug was not in at all.
But there is about 3 inches from the bilge to the bottom of the drain plug, and with water up to that drain plug, it would stretch out over a foot wide.

I just prefered not to have any standing water in the bilge, even if its only a couple of inches.