spark plugs - water damaged

[exrescueswimmer]

i have 8.1 mercruisers. the stbd engine has been running increasingly rough lately and has only gotten about 3200 rpm for a while so i had the plugs replaced because the mechanic had stated before they were the wrong ones anyway. he came back and said 3 and 5 were water fouled. i dont know very much about the engines so i wanted a little advice. first, what could cause this sort of thing? this past summer, the same mechanic replaced all 4 manifolds (port and stbd). second, could the manifold replacement be a contributing factor? finally, could this lead to the dreaded vapor lock? if that's the case and you are out, how do you identify the issue and what is the correct procedure?
thanks guys!

 

[SCORPIO]

Can't speak to your specific engine, but generally water doesn't "foul" a plug, it will either blast it clean, looking like its been steam cleaned, or it causes them to rust. Is this on the outer electrode or on the part screwed into the head? If interanl, that indicates you're getting water in the engine (BAD). It sounds like these are adjacent cylinders on the same bank. Are they located directly under the riser? You could have a riser/manifold gasket leaking allowing water to enter thru the exhaust valves. A blow head gasket can also let water in. As I said I don't know your particular engine, but these suggestions apply to most all V-8s.
I doubt that this is causing vapor lock which is boiling of fuel in the fuel lines/fuel rails.

 

[my3sons]

i have 8.1 mercruisers. the stbd engine has been running increasingly rough lately and has only gotten about 3200 rpm for a while so i had the plugs replaced because the mechanic had stated before they were the wrong ones anyway. he came back and said 3 and 5 were water fouled. i dont know very much about the engines so i wanted a little advice. first, what could cause this sort of thing? sea water or coolant getting into the cylinders.
this past summer, the same mechanic replaced all 4 manifolds (port and stbd). second, could the manifold replacement be a contributing factor? anything is possible, but only if he screwed something up, like cracking a manifold or leaving out a turbulator. You didn't mention the elbows, did he change those? they are stainless and usually hold up well, but if one had a bad weld, and it was put back on, that would not be good. finally, could this lead to the dreaded vapor lock? water in the cyls can cause hydro lock, yes if that's the case and you are out, how do you identify the issue and what is the correct procedure? Don't use the boat until you know what's going on. Hydrolocking the motor is when the piston tries to compress the water in the cylinder, and of course it does not compress. It usually results in bent or broken rods and pistons and holes in the block. Did you overheat the motor at any point prior to this issue cropping up? Is it using any coolant? Not knowing any more than what you stated here, my next move would be pressure testing the cooling system, then a compression test
thanks guys!

Sorry to hear about the problem, good luck, and keep us posted.

 

[Jimmy Buoy]

It is very unlikely that your new exhaust manifolds would be shot already, but are you sure that the mechanic installed the turbulators? (item 19 in the following attachment) http://www.perfprotech.com/mercruis...l-elbow-and-riser/assembly/7460/150?model=376

Without them, reversion may be possible causing water intrusion.

The 8.1 uses "dry joint" engineering as seen in the attachment, so it is virtually impossible for any cooling water to "leak" into the cylinders from a gasket.

If you had a blown head gasket you'd be losing antifreeze since the 8.1's are are closed cooled blocks. That doesn't seem to be happening.

If it were my engine, I would start by completing a simple compression test. Also, if you still have the old plugs post good photos of each one and let your fellow CSR members comment.

Have you run the boat since replacing the plugs are are you waiting to get more info first?

 

[exrescueswimmer]

thanks for responding.
i have not run it yet - was more concerned with causing bamage until i get to the bottom of the issue.
i'll take some pics of the plugs and post what if find out next. the consensus seems to be compression testing.

 

[exrescueswimmer]

well - he feels because there is evidence of prior overheating that it is likely to be the head gasket. we'll also do some pressure testing.
i'll let you know what the outcome is...

 

[exrescueswimmer]

thought i'd close this one out. we did the pressure test and there was a very small crack in the riser. replaced the riser and that engine is running better than ever!
thanks for all the advice!

 

[Jimmy Buoy]

Well that's a whole lot better than a head gasket! The risers on mine are stainless steel and this is the first time I've heard of one cracking - just goes to prove that anything is possible...

Thanks for the update.