water on spark plugs???

[dfrants]

got a 8hp mariner, its a Yamaha built one, model 6G1-L-308585. pulled the plugs out and all around the threads is this milkly fluid. both cylinders test around 130 psi compression. how does water get in? motor seems to run pretty good.

 

[quicktach]

Is the milky fluid something like lubriplate that's been put on the threads?

 

[dfrants]

not sure...I cleaned both plugs and will try running the motor again tomorrow.

 

[Chinewalker]

Water comes from two places. It's either a leak in the cooling system somewhere (.ie a bad gasket in the exhaust manifold) or it's in the fuel (ethanol gas tends to hold a bit).

 

[dfrants]

No Title

ran the motor again today, left one plug just finger tight for 2 minutes and this is what it looks like...

 

[Texasmark]

Never saw anything like that on a plug in that location. Looks like an oil and water mix....homoginized lubrication and water. I noticed your threads were clean so it doesn't seem to be coming from inside the crankcase wicking up the threads, even without the plug being completely tight. The water jacket cover that covers the entire rear of the block has holes right around where the plugs mount and those gaskets do leak cooling water after 10 years give or take.

With the plug(s) out, wipe everything clean, plug and the block "landing" where the plug seats. Put the plug(s) back in with the normal torque, run your 2 minute test again. Take 2 pictures: One from about 30 degrees out from behind the plug looking at where the plug seats against the block (landing covered by the plug) and another of the landing straight on where the plug was mounted after you take it out.

 

[dfrants]

No Title

its definitely coming from inside the cylinder...do I need to pull the powerhead to replace the bad gaskets? I'm just surprised that it still runs with this happening.

 

[Texasmark]

I see only one gasket and plate over the cylinders telling me it's typical Merc design of incorporating the head in the block casting. The plate is just the water jacket plate.

Get a flashlight and pull both plugs. Look through the spark plug hole onto the crown (top) of the piston. What does the crown look like, aka shiny, or black and scaly? Do both look alike?

Has this engine seen salt water. It looks pretty clean so it must have been well cared for. What year is it? I can't cross the serial number. Maybe Faztbullet can and will. Thinking about corrosion punching a small hole in the cylinder wall.

Does this engine run on pre mix or does it have a built in oil system? If premix, what is your ratio? What oil do you run? How long have you had it? How often do you run it. Since it's early fall, doesn't really matter your geographical location....Alaska, Hawaii sort of thing.

 

[dfrants]

I'm in MN. Freshwater only. 50:1 oil mix. This is a Yamaha built Mariner. I also have a Yamaha 8hp that looks identical to this one. I just got it. So I don't know its history. Best I can see, it looks clean inside both cylinders.

 

[dfrants]

It's a 1984 model.

 

[Texasmark]

I'm in MN. Freshwater only. 50:1 oil mix. This is a Yamaha built Mariner. I also have a Yamaha 8hp that looks identical to this one. I just got it. So I don't know its history. Best I can see, it looks clean inside both cylinders.

"Clean" how clean? Spotless? If so, you are getting water in the cylinders. The picture of the plug you showed in an earlier picture had a lilly white ceramic. Was that a new plug or did you clean it up that good or did it come out of the engine that way? Both cylinders, piston crowns, spark plugs look the same or just one?

Fresh water only reduces the possibility of a corrosion hole in the side of the cylinder letting water into the combustion chamber.

Water from fuel. Water from condensation formed when trolling for extended periods of time with no thermostat.....I didn't see one in your pics. Minnesota spells lots of cold running, condensation buildup.

After you answer these questions tell you what. Get a fresh tank of premix with a heavy dose of Sea Foam and take this engine out on the water and open it up and run it for about an hour at WOT. Bring it home and pull the plugs again and look at them and the piston crown.