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Fed up with oil drain plug leaking on Mercury 25.


Raycaster
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I posted before about my saga of performing a simple oil change on my 25hp Mercury that just has never been fixed. I went to properly torque it to spec like I’d done 10x before and the wrench went right around without stopping…

My auto mechanic “re-tapped” hole and used a larger drain plug that looked and tightened great but… nope, still leaked.

Have tried ever washer material possible including the Mercury $10 washers…

On the next oil change I was going to gunk it up with gasket goo but its just another patch. I hate launching my boat and seeing 1 drop of oil hitting the water that quickly spreads and looks like I’m dumping gallons. I’m losing very little oil but it still looks bad on the water.

So, I’m hoping to find a pro that can do a heliCoil or Sert properly that fixes it once in for all. If there is anyone in the Hamilton area that is up to the challenge let me know and pm me with availability and how many banks I have to rob. Lots of guys say its not a tough job but its not something I want to tackle.

Edited by Raycaster
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Thank you for the suggestions.

I have made atleast 10 different custom washer gaskets using several different materials (cork, rubbers, neoprene, etc.) without success.

Not sure why I have not tried teflon tape yet, will try for sure but I need a 100% solution. I use the 25hp for trolling so I try to give it 2-3 changes a season.

 

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On 9/5/2022 at 4:34 PM, spincast said:

Fwiw.  Heliocoil is pretty common for motorcycle engines for the sparkplugs.   If you can't find a marina to do it, try a motorcycle shop.  

Tapping is not the way to do it and results in what you are experiencing.

Teflon may help you but other than that I would not take it to a marine shop, I would take it to a place that works on dirt bikes and motorcycles because they likely have more experience doing the helicoil.

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8 hours ago, Podric said:

Tapping is not the way to do it and results in what you are experiencing.

Teflon may help you but other than that I would not take it to a marine shop, I would take it to a place that works on dirt bikes and motorcycles because they likely have more experience doing the helicoil.

Helicoils are relatively easy to install. The issue in this case would be all the filings from drilling the initial hole before and then tapping, and last but not least breaking the tab off to fall inside after installing the helicoil. A flush would work some what but might as well limit it in the first place. Greasing the flutes and only going a turn or two at a time, then removing, cleaning and reapplying grease would help for sure. I had to do that when chasing the threads on one spark hole on a quad I bought. It seemed to work quite well, the grease really held the filings well. That being said, seeing as the hole had already been tapped out to a larger thread, unless it was a real loose fit I see no reason to install a helicoil in the first place. Have you tried to wiggle the plug to see how tight the threads feel like half way in?

As I mentioned earlier, it's the gasket that does the main sealing, without it no plug will seal.  Raycaster, I would still suggest using an brand new OEM seal for sure, at the least you know it's made from the proper material that withstands oil and compression. With a larger plug it would be a bit smaller but should function. This is unlikely, but I would also check both faces the gasket touches and make sure both surfaces are smooth and flat.

So let's say that leaves the threads as the culprit. But then, why didn't the new plug fix that initial issue? hmmm...  hehe :) Then teflon tape should do the trick. It might not take a lot, maybe three or four turns depending how much it's stretched. I'd advise to cut a narrow ribbon no wider than the thread length. Be sure to wrap in the opposite direction of the thread going in and stretch it as you do. If you can secure the head of the plug even better to get a tight wrap before install. I speak from extensive experience for 13 years as a tech testing, fixing, calibrating and certifying pressure and vacuum gauges for aircraft and test equipment for all the First Air bases across Canada.

Good luck. Cheers

 

 

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A heli-coil would work and you can probably find one with the same thread pitch as the original drain plug.  It will actually be stronger than the original threads into aluminum.  Try to reduce the amount of shavings that go in the hole, but if a few go in its no big deal as the drain is quite a distance from the oil pump pickup which won't be a concern unless you stand the motor on its head.  It will be money well spent to bring this to a small engine shop ( ATV's) as this is a common repair for them.

 

One oil change halfway through a season if you run it every day is plenty.. you can go 200hrs on oil without worry.  Marine engines don't see dust and dirt that other engines do.

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