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Any suggestions, or is it a "Merc" thing? I bought this boat/engine last June, and it has ALWAYS leaked/dripped oil/gas into the motorwell when the engine was tilted up. I found a fuel hose with a hole in it and replaced it. The rest of the hoses were replaced this winter and the whole engine gone over by my mechanic. During the first run of the season, no oil leaked trailering from home to the ramp (8 miles). No oil leaked during the run, no oil leaked during the trip home on the trailer. I left the motor partially tilted up while I cut the grass where I park the boat. After 45 min, OIL in the motorwell! I cannot tell where its leaking from. A friend of my brothers had a Merc abou the same age as mine, said get used to it, his leaked as well...no way to stop it. What's the deal!

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I had a mariner that is basiclly a merc and it did the same thing. I am assuming your motor is oil injected since you say it is oil leaking. With the cowl off can you not pinpoint the source of the leak? I would start at the lowest point and follow it up wrapping each connection with a small piece of paper towel. Once you isolate the origin of the leak you will have a better idea of how to deal with it. I just accepted it.

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Gacto mine does all the time as well as many othes. I took out the tank to investigate. I replaced the o ring in the cap and that helped. Once I did i filled it with water and turned it over with no leaks. I did notice the neck is a little warped though and the cap doesn't fit a hundred percent. I was told they warp and they usually leak. I would start with the o ring and hope for the best!

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This is a very common problem. You don't say what Mercury you have but if it has an oil tank on the powerhead itself, there is about a 99 percent chance the cap is the culprit.

Replacing the gasket might help but the caps crack right where the sides meet the top. This is the result of age and overtightening.

Just replace both the cap and the gasket.

It is also a good time to replace ALL the oil hoses if the motor is oil injected. It's about $20 in parts. Just do it.

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I had the same problem with the tank cap. Mine had the old style tank with the rectangular fill. I replaced the tank with the round fill with the o-ring but I noticed that when you tighten the cap the neck would expand. I put a hose clamp around the neck of the tank where the cap goes in and just made it snug. Now when you tighten the cap the o-ring can't expand the neck of the tank. It works very well. I have had no leaks since. Also, it is not necessary to crank down on the filler cap. Only enough to seat the 0-ring. Another source of oil on these Merc's is the carbs. Mine used to leak from the carb throats every time I tilted the motor up. I found that if I let the motor idle for a minute before shutting it off it stopped the leak. I also devised a system to catch any oil that drained from the carb throats. If you are interested send me a pm and I can go into detail. In any event, I now have a 94 Merc 90hp that does not drip oil all over the boat.

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Thanks for the info guys. I will check the cap and oring, and replace them. It's a 1988 70hp with oil injection, has the tank on the power head like Tom described. Every hose in the engine was replaced this winter. I had it completely gone over so I knew what I was dealing with. When the bill came, i was unsure if the motor was worth it. Mechanic said it was like a new motor...and it does run like one. Only it leaks oil like a dump truck! I keep you posted on how it goes.

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Is your merc a two stroke? I have a oil injected 2004 75 hp merc elpto and it did the same thing too. I thought it was oil from the resevoir. It was not. After I took the cowling off and raised it up and lowered it a few times the resevoir never leaked. It was the bottom carb. I could see it pouring right out of there. I did not use the boat much over the winter since I was re-doing the inside and outside. A few weeks back I put fresh new gas in the tank and went and ran her for a few hours. I went a total of 40 miles and it ran great. Now for some strange reason it doesn't leak when I raise it up. Not sure if something in the carb was stuck open or what. It is very strange to me. Maybe it just needed to be ran for a while. Good Luck.