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Old 23-11-2011, 11:57   #1
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Yanmar Saildrive Seal Leaking . . . Again

I have a 1 1/2 year boat with Yanmar 3YM30's w/SD20 saildrives. After less than a year, one engine had a leaking saildrive seal (actually the seal between the engine & the transmission). It was fixed under warranty & due to my internet searches , I "persuaded" them to install an "overflow tank set-up" - basically a fitting from the top of the saildrive to a small reservoir - when excess pressure builds up in the saildrive, air and/or oil can escape thru the tubing into the small tank. Read that some people had to resort to this after several saildrive seal failures. Apparently, Yanmar allows (& sometimes pays for) this modification, but officially says it's completely unnecessary.

Jump forward to the present. Both saildrives are now leaking from the same seal. Yanmar may replace both seals, still under warranty, but nothing further. Obviously, there is a design defect or defect on these engines that is causing 3 seal failures in only 1 1/2 years. Many have said that the overflow tank would help, but seemingly not.

Does anyone have any further insights into this seal failure problem and/or any contacts at Yanmar? I am dealing with Mack Boring in NJ (NE distributor), Mastry in FL (SE distributor) & Marathon Boatyard (who repaired the one seal already).

Thanks.
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Old 23-11-2011, 12:02   #2
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Re: Yanmar Saildrive Seal Leaking ... again

I'll make a posting so I can follow this subject along. ...be interesting to see if there are many other similar instances. Have you done a google search for 'saildrive leaks' or 'saildrive seals' ?
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Old 23-11-2011, 12:41   #3
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Re: Yanmar Saildrive Seal Leaking ... again

To which seal exactly are you referring? Is it the shaft seal inside the saildrive housing on the upper saildrive shaft? What happens when it leaks - does it drip oil out of the bell housing? I don't know of a seal between the engine and transmission.

Mark
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Old 23-11-2011, 13:27   #4
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Re: Yanmar Saildrive Seal Leaking ... again

Mark,

Marathon Boatyard called it the saildrive seal, but that may not be correct. It is the seal between the engine & SD20 saildrive & yes, the oil does drip between the two at the bell housing. I can contain the oil if I put several folded paper towels under that joint (replacing them every few hours of running). I saw the replacement seal briefly - I recall it looked like a 10" diameter black "donut". To replace it, the engine has to be detached & lifted back from the saildrive.

Thanks.

Russ
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Old 23-11-2011, 14:26   #5
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Re: Yanmar Saildrive Seal Leaking ... again

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Originally Posted by Ortolan View Post
Mark,

Marathon Boatyard called it the saildrive seal, but that may not be correct. It is the seal between the engine & SD20 saildrive & yes, the oil does drip between the two at the bell housing. I can contain the oil if I put several folded paper towels under that joint (replacing them every few hours of running). I saw the replacement seal briefly - I recall it looked like a 10" diameter black "donut". To replace it, the engine has to be detached & lifted back from the saildrive.

Thanks.

Russ
The seal that keeps oil from leaking into the bell housing is a lip seal on the pinion shaft. It's far from 10" in diameter, did you mean 1" ???
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Old 23-11-2011, 15:12   #6
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Re: Yanmar Saildrive Seal Leaking ... again

Yes, I'm sorry - That is it - Mini-donut size - I only got a one second look at it in a bucket of oil as the mechanic walked off.

Russ
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Old 23-11-2011, 15:34   #7
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Re: Yanmar Saildrive Seal Leaking ... again

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Yes, I'm sorry - That is it - Mini-donut size - I only got a one second look at it in a bucket of oil as the mechanic walked off.

Russ
If you are keep taking out these lip seals, there is an issue causing it, they should last 1000s of hours. Mine are 8 years old, 1800 hours, no leaks.

I have never understood putting the 'overflow' tank on the saildrive. The unit is 2/3 in water, thin aluminum between the oil and water, the oil can't be more than a couple of degrees different than water temp. Yes, a small temperature change will cause a slight pressure inside the saildrive, but nothing near enough to push oil past a lip seal. After all, a lip seal get tighter with pressure (if installed properly - spring towards the oil!).

Something else is going on, a misalignment causing extra heat generation?
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Old 23-11-2011, 15:39   #8
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Re: Yanmar Saildrive Seal Leaking ... again

Did the mechanic insert the seal in the correct orientation? Put in backwards would allow oil to leak out.

Mark
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Old 24-11-2011, 16:09   #9
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Re: Yanmar Saildrive Seal Leaking ... again

Mark -

Don't know if he installed it correctly (after all - he started up the engine & ran for over a minute before realizing that he hadn't turned the cooling water intake back on again ....), but that was only 1 of 3 seals - The original seal on that engine & the seal on the other engine were factory installed.

DotDun -

The high temp of oil is an interesting possibility - I'll try to "take it's temperature" after a long run next week. The "overflow" tanks on my engines may be helping/needed, as for some reason, the oil does expand greatly.

Even when I picked my boat up brand new, the plastic oil caps had been tightened with pliers & when loosened, oil would leak out. After my first seal failure, I drilled & tapped the oil caps with fittings, clear tubing & a water bottle - oil did back up at times about 2' up the tubing. Once Yanmar installed their fittings into the sail drive top, oil has spurted up both tubes into the little tank (only a tablespoon or so, but plus what's in the 3' of tubing). All of this is with the oil level at the lower end of scale.

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Old 24-11-2011, 16:38   #10
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Re: Yanmar Saildrive Seal Leaking ... again

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The high temp of oil is an interesting possibility - I'll try to "take it's temperature" after a long run next week. The "overflow" tanks on my engines may be helping/needed, as for some reason, the oil does expand greatly.
First, this begs the question, the oil is clean and not milky, correct? (milky = water)

Second, you are using the correct oil, 80-90W - see attached.

Third, can you 'redline' the engine in gear? (or are you over-propped?)

The proper oil level is about 1/2 way up on the pinion shaft. There is air in the top of the housing that will compress ever so slightly as the oil temp goes up a couple of degrees. There is an 'oil pump', #41 in the above diagram, that slings oil up thru the top cap (thru o-ring #23) to lubricate the top bearing.

This is a relatively simple transmission, unless you have it overpowered or something wrong, it shouldn't run hot enough to push oil out through the seals.
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Old 24-11-2011, 19:44   #11
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Re: Yanmar Saildrive Seal Leaking ... again

I installed expansion tanks on my SD20 eight years or more ago, and have definitely seen the oil levels rise and fall. After long runs, the oil does get warm and the level rises. I expect there is a certain amount of heat transfer from the hot engine itself to the leg.

To me, an expansion tank makes a lot of sense.
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Old 24-11-2011, 20:59   #12
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Re: Yanmar Saildrive Seal Leaking ... again

The expansion tank is more for the seal at the shaft. I understand it is supposed to create a positive pressure to not allow seawater to enter the system if the propshaft seal fails. The seal between the engine and the sail drive should last a thousand hours or more unless there is an alignment problem.
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Old 25-11-2011, 08:10   #13
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Re: Yanmar Saildrive Seal Leaking . . . Again

Oil is clean & no water - I hauled boat & drained drives last summer, carefully checking for any water. Yes, using 80W-90 gear oil. Don't believe I'm overpropped - 3,800 is wide-open, which I only do for about a minute or two per month. I've been told by some that this seal leaking is only common on boats run too hard/hot for long periods, but 80% of the time I'm running 2,600 RPM / never over 3,000 for more than 1/2 hour. Ever since oil started to leak from the filler cap (before any of the expansion tank set-ups), I've kept the oil level near the lower end of the range.

Fustrating, as I can't get any answers from Yanmar, their dealers or distributors. Assuming they replace these 2 seals under warranty, I certainly can't afford to replace 1 or 2 seals per year on my own dime ($800 per seal???).

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Old 27-11-2011, 07:42   #14
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Re: Yanmar Saildrive Seal Leaking . . . Again

TEMP UPDATE:
After 6 hours of run-time at 2,600 RPM, the saildrive oil temp in both engines was 106 degrees. That's lower than I would have guessed. Not sure if the temp raising from 70 to 106 degrees should expand than much & why the expansion tank shouldn't be able to deal with it. Also curious is why there is a "pissing" when I unscrew the oil fills (when the engine is hot) - the fitting in the saildrive top plate (installed by Mack Boring/Yanmar) with the tubing & expansion tank should be dealing with any pressure...

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Old 27-11-2011, 09:43   #15
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Re: Yanmar Saildrive Seal Leaking . . . Again

I might have missed something in your previous posts, so forgive me if I have.

I would think that much temperature rise could expand the oil enough to cause issues. Can't explain the hiss since you now have the exp. tank. Mine did this before I installed the tank. All of the varying expansion rates--oil, steel, aluminum--to my mind would create positive or negative pressure differentials.

How high is the oil level in the expansion tank relative to the waterline? Mine is between 1.5 and 2 feet above waterline (oil is lighter than water, but I didn't run the calcs on S.G. and the fluid depths, but I figured this was plenty high to keep a positive pressure inside the leg).

Where is the tubing tapped into the housing relative (height) to the filler cap? I'm trying to picture how Mack did yours. I told Mack what my plan was years ago in case they could foresee a major problem, and they didn't discourage me from doing it.

WRT possible water intrusion, I use an Amsoil synthetic product that they claim can tolerate 10% water. Can't hurt.
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