MCM260 5.7L rust on spark plug

[tfret]

While changing my spark plugs this weekend I noticed that I have rust on my no.5 plug. Not a lot of rust, but rust none the less. What does this mean?

 

[TilliamWe]

Re: MCM260 5.7L rust on spark plug

It means you are getting water into that cylinder. THAT probably means you have an exhaust system issue. Good luck.

 

[Bondo]

Re: MCM260 5.7L rust on spark plug

Ayuh,... My 1st WaGuess is the riser/ manifold joint/ gasket is failing,...

Especially if ya boat in the Brine....

 

[tfret]

Re: MCM260 5.7L rust on spark plug

The boat has only been in fresh lake water. Do I need to pull the riser and exhaust manifold to inspect? I really need some guidence here. I don't fully understand how the water and exhaust combine, I've never taken it apart before. I just need to know how it works and where to start looking for problems. Thanks!

 

[Bt Doctur]

Re: MCM260 5.7L rust on spark plug

6A-9 thru 6A-12
http://www.boatfix.com/merc/Techbk/97/97hga6.pdf

 

[tfret]

Re: MCM260 5.7L rust on spark plug

After spending some time searching this forum i've gotten quite an education. Seems that the riser to manifold gasket could be leaking into the exhaust chamber and running down to the engine block. That is easy enough to pull and replace. Would it be wise to pull the manifold to inspect it too, or is manifold failure far less likely in fresh water.

 

[wire2]

Re: MCM260 5.7L rust on spark plug

While changing my spark plugs this weekend I noticed that I have rust on my no.5 plug. Not a lot of rust, but rust none the less. What does this mean?

I expect you're talking about rust on the part of the plug inside the combustion chamber, not on the outside shell, correct?

 

[tfret]

Re: MCM260 5.7L rust on spark plug

Yes, the rust is on the "rim" of the plug opposite the end where the wire connects. The rim seats against the head when screwed into the hole. Indicating water getting into the cylinder. The compression is tight on cylinders so I don't expect a head gasket.