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-   -   venting oil in a saildrive? (https://www.cruisersforum.com/forums/f54/venting-oil-in-a-saildrive-247688.html)

SailSB 07-03-2021 18:45

venting oil in a saildrive?
 
I have yanmar saildrives and have replaced the seals recently after a small amount of water intrusion.

A friend with what I believe are SD60 saildrives has suggested that there is an inherent design flaw in the sealed oil system and has retrofitted his with a cap where the dipstick usually is that has a feedthru to a pipe which leads to a vented container (kind of like for radiator fluid on a car)

The idea is that as the oil heats up during use of the saildrives, the oil and air around it expands, then when it cools down, the pressure drops and the only place for it to pressure compensate is to pull in water thru the seals. With the vented system, the oil could expand and overflow to the container, then when it cools down, it can pull the oil back into the sail drive.

This makes a lot of sense to me. have any of you done this? is there any negative to this system that I am not thinking of? It seems like a great way to avoid overfilling or underfilling since there would be a large buffer in the vented container.

Thanks for any thoughts.

Ken

HeinSdL 08-03-2021 07:02

Re: venting oil in a saildrive?
 
Hi SailSB, maybe I can share what I discovered on this topic, having an SD40 on my boat.

I heard about the 'design flaw' some time back and I initially discovered that it was important to not overfill with oil. Later the reasoning became clear in that too much oil means too little compressible air so that when the temp in the unit goes up meaning expansion of the oil, the air pocket would accomodate the expanding oil without excessive pressure increase. But add too much oil and the seals might get stressed too much leading to leaks.

I had a leak on the input shaft on my SD40 resulting in oil dripping out of the bell housing on the 4JH3E. So I replaced the seal there and.... installed the air vent you mentioned. It's a tube connected to one of the filling ports on top of the SD40 which then goes up a foot or so above the unit (in fact, ends up above the waterline). In my case it's just an air vent meaning pressure inside the SD40 remains atmospheric and the problem of stressed oil seals is resolved*.

Some users have installed a header tank, thereby filling the unit in its entirety with oil and you are able to monitor any leaks by observing the oil in the header tank. I have not done that. I am happy with my solution for now and am not sure if the SD40 completely filled with oil does not introduce new problems (though you do have to reverse one of the lower seals since the pressure differential is now also reversed with the header tank).

If you want the email address of a chap in the US who knows all about this let me know.

*At least I hope so. My boat has been out of action for 12 months now, since the SD40 mod, due to covid difficulties...

Jahwork 09-03-2021 15:07

Re: venting oil in a saildrive?
 
4 Attachment(s)
Hola,

Below is a cut and paste of a post to a similar question from a while back. It has worked flawlessly since install and I am very happy with the results.
I have also added my new sign off/disclaimer which did. It appear on the original post as it seems only appropriate considering many of the responses and PM’s I have received.


Hola all,

After selling our Lagoon and purchasing a serious “fixer upper” cat I am in the process of a complete all-systems rebuild/replace. After removing the engines and saildrives for rebuilds, seal/diaphragm replacing, and a bunch of other work I decided to construct an expansion tank system. Here is what I did: after much legwork and searching I was able to source a 316SS hydraulic plug of the same thread type/size as the original yanmar plastic one which then also uses the same size O-ring for its seal. I then drilled a hole in the center and tapped threads to receive a 316SS 1/4 inch hose barb fitting. I found some universal plastic overflow tanks on amazon with 1/4” barb on the bottom and vented cap for around 10-20 bucks each. A piece of 1/4” fuel hose and a couple stainless AWAB clamps to finish her off. The pics are a little dark, I apologize as I had to be my own lighting operator and photographer. I have trouble multi-tasking. Just an option for those considering a similar system. I am sure there are both different and better ways to achieve the same objective. This is just one.

Oops, I forgot to add that I installed the custom “black sharpie” oil level line indicator to assist me in checking it easily at a glance.

And since some then requested info on what I used and from where it was sourced.....

Hola again,

Sorry I should have included these earlier.

The stainless hydraulic plugs are sold on amazon as these:

Joywayus M33x2 Thread Stainless Steel Rods by CNC Hex Head Corrosion Resistant Plugs Pipe Fitting

The tanks I purchased are these from eBay:

Universal Radiator Coolant Reservoir Bottle Overflow Tank Dorman 603-001 New

The hose barb fittings are easily sourced from either amazon or eBay depending on what size threads you desire. I used 3/8” thread and 1/4” barb I believe.

Sorry couldn’t get links to work or I am too stupid to figure it out. Most likely option 2 is correct. If you search the above they will lead you to what I purchased.

The hydraulic plugs are solid stainless and quite thick so drilling them is a a little bit of a chore. I have access to a large metal lathe which made it easier to drill and tap for the threaded hose barb fitting.

Hope that was at least mildly helpful.

Safe Journeys!!
~Jake

To alleviate the need for the supreme and almighty sailing masters among us to belittle, demean, ridicule, chastise, criticize and in general respond in their usual condescending fashion I will readily admit that everyone here, and most likely everyone everywhere in the world, are much smarter, faster, stronger, better looking, more intelligent, more experienced, more well travelled and in general are much better members of the global society than I could ever dream of being. Please disregard any and all of the above prose, as well as the below pictures, in favor of only listening to the self professed experts among us that are so amazing and magnificent that they have absolutely nothing to be learned from anyone or anything else as they clearly already know all that can be known. Oh and since I haven’t “been there” or “done that” then I am obviously not afforded the opportunity to have an opinion, or so the sailing elite here have informed me. Since they obviously have been everywhere and done everything it appears that they and they alone are allowed the luxury of stating their opinions........oops I forgot they don’t have opinions as they are so smart, whatever they say is fact and shall not be disputed.

Congratulations!!! You win. I lose. I shall now sulk away in shame.

Safe Journeys to most,
~Jake

ggray 09-03-2021 20:32

Re: venting oil in a saildrive?
 
I installed header tanks my SD20s probably 19 years ago. I think is the way to go on one of these saildrives.

My tanks are about one foot or more above the waterline, keeping a slight positive pressure on the seals. Just venting to the atmosphere doesn't relieve all pressure on the seals as there is more water pressure on the seals (what, maybe 2 feet down) than there will be oil pressure (maybe 1.5 feet of head of a less dense liquid). I want a slight pressure inside to keep the water out.

Jahwork 09-03-2021 21:09

Re: venting oil in a saildrive?
 
Yes, I should have included that info. Thank you for reminding me. Due to the constrains of my small engine spaces I was able to get the tanks about 18” or so above the waterline. I would have preferred to have it higher but that is all I could achieve due to my vessel design without sacrificing living space. So I am happy to hear that your tanks with a 12” head have performed well for 19 years. I hope to get similar results.

BillKny 09-03-2021 21:25

Re: venting oil in a saildrive?
 
Looking at a mechanically very similar system: my outboard.

The lower unit is full to the very top (no significant air space) with oil. When running at speed it gets hot. Oil does not leak out. When it cools down water does not leak in. It works for hundreds of hours like this. This is true for outboards of WAY higher horsepower than the typical saildrive system.

Why does this seem to be an insurmountable problem with saildrives?

Jahwork 09-03-2021 21:39

Re: venting oil in a saildrive?
 
I am unsure the problem of which you speak. Perhaps others have a similar issue to overcome not unlike that of which you surmise. My intent, design, fabrication and install was not related to the problem you seem to have significant concern over. So a simple and less prose prone answer to your problem is that it simply is not an insurmountable problem for saildrives, nor do I believe it to be so in traditional lower unit/gear case design, at least so be the findings in my limited and feeble existence wind experience. The experiences and findings of others I am sure are both different and of greater significance and import than any I could bring to light. My diatribe, and subsequent actions, should be construed as nothing more than a prophylactic response as an affront of this simple minded lesser educated commoner to assist in minimizing, mitigating and reducing the potential occurrence of future concerns. I have no doubt your concerns are not without merit.

To alleviate the need for the supreme and almighty sailing masters among us to belittle, demean, ridicule, chastise, criticize and in general respond in their usual condescending fashion I will readily admit that everyone here, and most likely everyone everywhere in the world, are much smarter, faster, stronger, better looking, more intelligent, more experienced, more well travelled and in general are much better members of the global society than I could ever dream of being. Please disregard any and all of the above prose, as well as the below pictures, in favor of only listening to the self professed experts among us that are so amazing and magnificent that they have absolutely nothing to be learned from anyone or anything else as they clearly already know all that can be known. Oh and since I haven’t “been there” or “done that” then I am obviously not afforded the opportunity to have an opinion, or so the sailing elite here have informed me. Since they obviously have been everywhere and done everything it appears that they and they alone are allowed the luxury of stating their opinions........oops I forgot they don’t have opinions as they are so smart, whatever they say is fact and shall not be disputed.

Congratulations!!! You win. I lose. I shall now sulk away in shame.

Safe Journeys to most,
~Jake

ggray 10-03-2021 06:03

Re: venting oil in a saildrive?
 
Quote:

Originally Posted by BillKny (Post 3361286)
Looking at a mechanically very similar system: my outboard.

The lower unit is full to the very top (no significant air space) with oil. When running at speed it gets hot. Oil does not leak out. When it cools down water does not leak in. It works for hundreds of hours like this. This is true for outboards of WAY higher horsepower than the typical saildrive system.

Why does this seem to be an insurmountable problem with saildrives?

Sure they are similar to each other, but the sail drive prop shaft is much deeper with a sail drive than an outboard propshaft, so is subjected to much more water pressure.

My sail drive is submerged 24/7 for two years or more, constantly subjected to this water pressure. Is your outboard? You say for hundreds of hours. Two years is 17,520 hours.

You say there is no significant air space at the very top. Are you sure? I doubt that the relieve plug (probably not the right term) is at the very top of the casing, and wherever it is there is a much larger surface area (therefore volume/height differential) than there is with a saildrive, where the top of the reservoir is just a very small air pocket, especially considering that the SD holds about 2.5 quarts or more. It's been suggested that lowering the oil level to increase the size of the air space helps, and that makes sense. But I like what I've done.


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