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mn_bowhunter

1988 Mercury 20 HP problem

11 posts in this topic

I took the boat out yesterday and when I went to start it I noticed exhaust gases coming out the pee hole. Once water started flowing I didn't notice it anymore. It was also a little harder to get going, I'm pretty sure slightly flooded. Should I be concerned about seeing exhaust come out of the water port? Thanks for any suggestions.

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I'm positive it was exhaust. Bluish tinted smoke, and the motor hadn't been started in over a week so it shouldn't produce steam on start up. I went out again last night and it didn't do it so I'm not really sure what to think. Also it has been dripping some unburned gas/oil mix from the prop. I doubt these are related, but just giving more info.

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I'm positive it was exhaust. Bluish tinted smoke, and the motor hadn't been started in over a week so it shouldn't produce steam on start up. I went out again last night and it didn't do it so I'm not really sure what to think. Also it has been dripping some unburned gas/oil mix from the prop. I doubt these are related, but just giving more info.

My 88' 45hp Mariner does the same thing. I've found that if I pre-mix a little rich that she does smoke a bit more and has some dark gas/oil mix that comes from the prop when I put her in the garage. I wouldn't worry about it. The engine is a little smokey but they are great engines.

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Unburnt Oil / Gas isn't a huge deal and is somewhat common, especially when mixed heavily.

I'd keep an eye on the exhaust out the telltale... it could indicate a gasket failure in the water jacket.

marine_man

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Excuse my ignorance, but where is the water jacket? I'm assuming it's the entire cooling system. Does the water go through the exhaust? Like I said before I only had this happen once, and last night I went out again and was paying closer attention and looking for bubbles in the stream that would indicate exhaust gases but saw none. The motor was slightly flooded when it happened. I choked it and it didn't need to be, so when it started it shot out much more smoke than usual then died. I flipped the choke off and it started the next pull and this is when the exhaust came out the telltale. Sorry if this is redundant, but I wanted to make sure I was clear. The unburnt gas/oil doesn't concern me as its only happened twice and that was with about a half tank of last years gas so I'm guessing that was the problem.

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The water jacket, and associated components is directly related to the cooling system. What I'm thinking could be happening, is the gasket between the water jacket and the head, or the gasket between the water jacket and the mid section is leaking.

midsection.jpg

The exhaust is returned to the water through the water jacket, and also provides the cooling water to cool your motor. If the gasket were leaking it's possible to get exhaust into the cooling water, although not something you see very often.

marine_man

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A bad exhaust cover gasket can also do the same. Exhaust gas pressure can overcome the pressure in the water jacket before water has reached the top of the block.

23-1.png

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The inner exhaust cover was bad for sure. I pulled the cover off and discovered some water/oil mix in the exhaust passages and around the lower cylinder. Just gotta round up new gaskets and put it back together to see if she's fixed. Anyone know the torque specs? Also I'm thinking this could be what's causing the unburnt fuel so maybe that will go away so I don't get any more spots on the garage floor. Thanks again for the help!

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