Should I drill lower unit water drain holes?

[JimMM]

I have a 1995 200 HP Mercury outboard on my deck boat … my lift won't always bring the lower unit high enough above the water to tuck it under and drain the water sitting in the exhaust hub. So it sits tilted up {sometimes for extended periods) and water just sits in the exhaust cavity creating corrosion in the area just behind and around the bearing carrier o-ring. I'm concerned that eventually it will get under the o-ring and cause a leak that would be difficult to fix as well as making it just that much more difficult to remove the bearing carrier for any future gearcase service.

So, I'm thinking of drilling two small drain holes (yeah, crazy, I know) about a 1/2" behind the bearing carrier o-ring, one on either side of the vertical bottom rib of the bearing carrier housing to allow water to drain out when the motor is tilted up. I think angling the holes slightly fore to aft going in from the outside bottom would keep positive pressure on the holes while the boat is under way to prevent exhaust from coming out the holes and going into the prop causing cavitation. I'm thinking of starting with very small (easy to patch if necessary) 1/8" weep holes but can work my way up if they get clogged too easily.

I'm not sure if this is a brilliant solution or a really bad idea. Thoughts and/or alternative solutions?

 

[Texasmark]

I don't know what a couple of ¼" or less holes would hurt. You could get that much agitation and bubbles from a keel. At higher speeds water pressure would seal the holes off. Holes wouldn't be all that much gas anyway so I doubt you would have any prop ventilation, like is experienced with high performance props with deliberate ventilation holes bored under the leading edge of each blade.

The area on the back side of the prop blade is a vacuum and that suction is what helps pull exhaust gasses out of the exhaust hub at low/slow speeds. The center of the bearing carrier area has no such vacuum so the potential for affecting prop performance is even less than I surmised, now that I think about it.

Funny, I keep my boat on the trailer in my garage with the engine vertical and one of the reasons is to drain the water to which you are referring. I can see how you could be concerned with a marina docking.

I guess your plan is to remove the prop and measure the back of the bearing carrier (where the Oring seal is housed) distance to the end of the casting, subtracting a 1/4" or so and My vote is Yes.

 

[jimmbo]

I'm not sure if this is a brilliant solution or a really bad idea. Thoughts and/or alternative solutions?

I would put in the Really Bad category, and I'm being Polite

However, it is your engine, so do what you want

 

[GA_Boater]

I don't think drilling holes is the way. I take it that you are in saltwater and drilling holes will expose raw aluminum.

What's wrong with your lift if it doesn't always raise high enough to lower the motor?

 

[Texasmark]

I would put in the Really Bad category, and I'm being Polite

However, it is your engine, so do what you want

Yepper. His engine, his idea, speculation that it will generate a problem later on.

 

[JimMM]

I guess your plan is to remove the prop and measure the back of the bearing carrier (where the Oring seal is housed) distance to the end of the casting, subtracting a 1/4" or so and My vote is Yes.

Yes, that is the plan. I figure can always JB Weld the holes closed if there are any bad effects. Even tilted down when the water is low enough, the large retaining nut that holds the bearing housing in, has a big enough lip to hold some water in there.

 

[JimMM]

I would put in the Really Bad category, and I'm being Polite

However, it is your engine, so do what you want

I'm still considering other possibilities. Any suggestions?

 

[JimMM]

I don't think drilling holes is the way. I take it that you are in saltwater and drilling holes will expose raw aluminum.

What's wrong with your lift if it doesn't always raise high enough to lower the motor?

I would zinc chromate and paint the exposed aluminum inside the hole. I don't think these holes would be any more susceptible to corrosion than the small speedometer hole in the lower unit. They would be dry most of the time.

The lift is supported by piles driven into the bottom which doesn't go up and down like the water level, i.e. it's not a floating lift..There are two bow tops that only allow raising the boat so far before they hit the underside of the roof.

 

[Chris1956]

A couple of observations. First of all, that is a 2 cycle motor, right? So you are pumping oil into the exhaust. That will protect the aluminum quite a bit.

Secondly, how many Mercruiser sterndrive outdrives are moored in saltwater? Millions? These are almost always mated to a 4 cycle motor, and are submerged in saltwater for the entire season. Did you ever hear of a failure like you describe? The mercruiser outdrive is very similar to your OB gearcase.

Drilling holes is unnecessary. Don't let it freeze with water in it though.

Spray the exhaust cavity with some freshwater to drive off the salt and relax.

 

[harringtondav]

My Alpha II won't drop completely when on the trailer. So I back the trailer over enough stacked 2x lumber to get the stern up high enough. ....may work for you.

Edit: I reread you OP. Is it possible to raise the bunks on your lift enough to clear the lower unit?

 

[GA_Boater]

I would zinc chromate and paint the exposed aluminum inside the hole. I don't think these holes would be any more susceptible to corrosion than the small speedometer hole in the lower unit. They would be dry most of the time.

The lift is supported by piles driven into the bottom which doesn't go up and down like the water level, i.e. it's not a floating lift..There are two bow tops that only allow raising the boat so far before they hit the underside of the roof.

"two bow tops" meaning a bimini? Can you lower the top before lifting the boat?

 

[Scott Danforth]

I would zinc chromate and paint the exposed aluminum inside the hole. I don't think these holes would be any more susceptible to corrosion than the small speedometer hole in the lower unit. They would be dry most of the time.

The lift is supported by piles driven into the bottom which doesn't go up and down like the water level, i.e. it's not a floating lift..There are two bow tops that only allow raising the boat so far before they hit the underside of the roof.

so you are too lazy to fold your bimini top down to raise the boat all the way out of the water and your best idea is to drill holes in the lower unit?

first, fold your top down and raise the lift higher
second hose the lower unit with a garden hose with fresh water.

 

[jimmbo]

Can the Roof be raised?

 

[GA_Boater]

Can the Roof be raised?

Was gonna make that suggestion until I reread and saw that the bimini is still raised.

 

[JimMM]

OK, it looks like the don't do its outnumber the go aheads. I asked and I never ask if I can't stand the answer, so no drillin' Thanks all for your opinions. Yes I am lazy. I have a motorized lift plus motorized drop sun curtains that come down around the whole boat to protect it from sun fading so I don't have to polish and wax it so often. As far as raising the roof, that would be more work and expense than just replacing the whole lower unit for a new one. As far as lowering the tops, there's two front and back and when they are down the bows block all the exits … plus I am lazy. I hadn't thought of the oil in the exhaust protecting the metal. Good point! If and when the clutch dog wears out and I can't get the bearing housing out, I"ll come back and curse you all out. (just kidding)

 

[flyingscott]

Oil in the exhaust will protect nothing oil floats on water.

 

[JimMM]

Oil in the exhaust will protect nothing oil floats on water.

True although I thought he meant the oil in the exhaust would "coat" the metal more like an oily soot. Which gave me an idea to use something that I've had great luck with protecting my aluminum trailer, something called Corrosion X. It basically waterproofs whatever you spray it on. I also sprayed it on the steel parts of the trailer and it dissolves the rust on the winch and protects it from further rusting. Don't know why I didn't think of this earlier, but I'm going to spray some down into the exhaust hub in the lower unit. Hopefully it will protect the metal and not adversely affect the rubber o-ring. Maybe I'll test it on an extra bearing housing o-ring. All the reviews I've read online about this stuff are positive for use on anything from boats, farm equipment, cars, guns, to I-phone electronics and RC car and boat servos. I think I'll try it on my JD lawnmower deck, those seem to always eventually rust from wet grass sticking to the underside in clumps and rusting out the metal. It's supposed to bond to "any metal" so we'll see how it does on the lower unit. Oh, they make a HD version that's thicker but I think I'll stick with the regular version and see how long it lasts. I can always upgrade the the HD stuff. Anyone have any experience with this stuff around marine metal parts? This is a link to the stuff https://www.corrosionx.com/ (no, I'm not affiliated with the company in any way)

 

[JimMM]

A couple of observations. First of all, that is a 2 cycle motor, right? So you are pumping oil into the exhaust. That will protect the aluminum quite a bit.

Secondly, how many Mercruiser sterndrive outdrives are moored in saltwater? Millions? These are almost always mated to a 4 cycle motor, and are submerged in saltwater for the entire season. Did you ever hear of a failure like you describe? The mercruiser outdrive is very similar to your OB gearcase.

Drilling holes is unnecessary. Don't let it freeze with water in it though.

Spray the exhaust cavity with some freshwater to drive off the salt and relax.

Thanks for the idea on oil protecting the metal. Gave me the idea to try using Corrosion X there. It's a water disaplacement/proofing penetrating thin film protective oil.

BTW, I've had Mercruiser stern drives moored in the water and the recommendation was to leave the outdrive down so the sacrificial anodes were in the water. That works. That's not possible with the current setup since the boat is on a lift and I don't want to leave it low enough to keep the lower unit submerged since the whole boat could float away if the water rises. The concern is the water trapped in the exhaust hub with the motor in the tilted up position. That water doesn't contact any of the sacrificial anodes such as the trim tab or the one on the intake ports. But thanks for the analogy.

 

[JimMM]

…
second hose the lower unit with a garden hose with fresh water.

Thanks you just reminded me that I have a Jabsco water puppy on board used to hose down the deck. It is self-priming so I guess I could jury-rig a wand to the intake to go down into the prop hub and suck out the standing water. I'm also thinking a good coating of Corrosion X would go a long way in protecting the inside of the lower unit exhaust hub as well.

 

[JimMM]

I took a spare bearing support housing o-ring and sprayed it with corrosion-x and after two days noticed no change. I believe it's a silicone o-ring, not rubber based. It's orange not black.

So I dried, cleaned and sprayed the inside of the exhaust hub with some Corrosion-X. I guess I'll see how long it lasts. Not a permanent solution, I know. I may also try the HD version which I've heard is very hard to get off so it should at least lengthen the renewal interval.