Yanmar SD50 oil level issues

[Knot Safety]

Folks

I am having an issue that is giving me no end of frustrations

Catamaran with two yanmar 3JH5E motors paired with SD50 sail drives. 1320 hours on both. Saildrive oils both changed out October 2019.

The port side sail drive oil level is perfect. Stays perfect. Oil is blueish. Starboard oil is giving me no end of frustrations.

I check the oil level each time before a big trip. Oil never appears milky at all but is considerably darker than port side oil. The problem is the oil level goes up and down like a yo-yo. One time it will be way above the full line, so I will suck a little bit out using a straw to siphon lift it into a clear plastic cup. If I get it perfect, then the next time there will be no oil showing on the dipstick at all. So I add just a tiny smidge to bring it up to the half way mark (takes hardly any oil to do). Run the motor for a bit. Next time oil is showing way above the full line. This transition happens every single time.

I checked it yesterday morning. Oil was below the dipstick. Brought it up to exactly half way on the hash marks. Ran the engine 3.8 hours. Today, the oil is way above the top hash line.

Two little things for you. Often when I open the oil cap there is a hiss of noise - sounds like air sucking in (but could be blowing). If I leave the cap off for five or ten minutes there is no noticeable oil level drop. Seems to stay the same. Also, the dipstick oil test always has air bubbles stuck to it whereas the other engine does not.

Thoughts/advice/guidance? I had been thinking it may be air bubbles getting entrained in the oil causing displacement up or down but that seems doubtful to have that much swing. If so, what is the solution? I am alert to the potential of water intrusion but if that is the case I would expect truly milky oil instead of just darker. And I would not expect the wild swings up and down in the volume.

For reference - whenever I have to add oil it is just a few ml. Barely anything. And I usually end up taking out nearly the same amount next time.

Okay give me your feed back

[tkeithlu]

Hmmmm. I can think of a few places to look, while an engine specialist may have experience with it that I do not.

It sounds as though you are pressurizing the crankcase on your starboard engine. It also sounds as though that pressurization is keeping more oil up in the engine and not sitting in the bottom of the crankcase waiting for you to measure it. I've never seen a pressurized crankcase, but maybe an engine specialist here has. Two sources for a problem could be your oil pump and leakage by one or more pistons.

Another possibility is a clogged oil line or filter. In that scenario, oil is being kept up top because it can't get down, and then does get by the clog when you run the engine.

Oil systems are supposed to be very free-flow, so everything settles very quickly when you shut down the engine. Your engine does not appear to do that.

I think that unless someone more knowledgeable than you or me on the topic has a better idea, I'd start by tracing the filter and oil lines, looking for a constriction to flow.

Good luck with it.

[Knot Safety]

Tkeithlu - thanks for the response. But just for reference - this is not the engine that is the problem. It is the saildrive oil level. Engine oil level remains perfect.

I will edit the post to make it clearer

For some reason it will not let me go back and edit the original post.

For all reading - the oil level referred to in the original post is the saildrive lube oil.

[tkeithlu]

Thank you, Knot. I apologize for getting the site of the crime wrong.

That is a mystery. Saildrives are gear boxes. I don't have one, but I'm not thinking conceptually different from an outboard foot with the addition of another 90 degree turn. Oil level should not be as critical as in an engine.

Another Hmmmm. What are the consequences of too much oil in your sail drive? In an engine it's pretty dramatic, as in bunches of exhaust smoke as the oil forces its way past the oil ring on the pistons. Done that, learned from it.

Hydraulic transmissions have maximum oil level, but I don't know what the consequences are. I don't know where oil could be hiding in a gear box. I'm tempted to say fill it with enough oil for it to always be above the minimum, and go worry about a problem that can bite you in the ass.

You monitor you boat very carefully. That's wonderful, and may get you out of a jam someday. I have to monitor mine fairly carefully, because it's a home built miniature ship, not a plug and play. My suspicion at this point is that this problem is not a problem, but I'm going to go check the transmission oil in my boat.

[ggray]

The problem could be caused by the closed /unvented characteristic of most (all?) saildrives. Certainly causes the hissing you hear when you remove the cap. Not sure about the varying oil levels, but that level can probably fluctuate a lot up at the top where there is little volume/surface area.
I have two 20 year old SD20 units. After a bout of water intrusion in one 18 years ago (and after I discussed with a Yanmar service center) I installed oil header/expansion tanks for each saildrive. I think that's helpful in several ways.

Maintains a constant (but minimal) positive pressure inside the SD, by mounting the tank a foot or so above the waterline. instead of pressure/vacuum fluctuations. And makes it easier to check/add oil.

[Knot Safety]

GGray - thanks. The positive pressure tank is definitely on the list of upgrades. As soon as I am at a place where I can find a plastic fitting to thread into the fill port. Currently in Antigua and they don’t have them here. If someone knows where to order I would appreciate it.

But back to the issue at hand. Today was the most oil I have had to pull out. And suspect that tomorrow morning will the the most I put in. The case was full. I took two pictures to show but can’t figure out how to attach them on here as I’m working from my phone.

To answer why it’s important to check the oil - SD50’s have a known issue of even slightly too much oil causing pressure build up and popping seals. And I know this drive has been acting weird so I am monitoring it closely.

Anyways - appreciate the feedback and look forward to hearing more.

[fortyninegroup]

Watch this video - he has solved the thermal expansion with a simple upgrade kit and it doesn't require a tank - https://youtu.be/ov1c6E3lcAM

[Cadence]

Originally Posted by Knot Safety

Tkeithlu - thanks for the response. But just for reference - this is not the engine that is the problem. It is the saildrive oil level. Engine oil level remains perfect.

I will edit the post to make it clearer

For some reason it will not let me go back and edit the original post.

For all reading - the oil level referred to in the original post is the saildrive lube oil.

I thought it was clear. I've never had one but believe there was a thread about the same issue.

[MartinR]

To me, especially since you get discolouration, this looks like a leaking seal between crankcase and drive.

[Knot Safety]

Thanks Martin. I had not thought of that and would appreciate some insight. If that had failed, would not the oil end up in the bell housing before it gets to the sail drive?

[Aqualibrium]

Any leakage from crankcase will come out of the bell housing drains! There is a significant void space between engine and gearbox where the flywheel is that prevents leakage of engine oil to sail drive and vice versa.
Quite a few years ago Yanmar issued a revised dipstick via a technical bulletin that lowered the oil level by app 15 mm. Unfortunately my copy is on my Cat which is currently in storage. Apparently pressure was building up in the air space and forcing oil past the seals???!!??
The best way to overcome this is to install an elevated vented header tank that is at a height to ensure leakage can only be out not in.

[arsenelupiga]

i have same engines and same problem, bit less hours. This is likely not a problem. To prove undo nut on top of saildrive and yellow stick to let oil level out. Wait couple minuted. Only then take measurement.

As mentioned before, best thing is to add depresurization, using that top nut a s a base. Oil gets hot and saildrive as well and expansion compression forces are considerable.

[Knot Safety]

Arsenelupiga - Okay. I will try that. Thank you. At least I’m not the only one having this problem. I thought I was losing my marbles.

Is that the little nut that is just off center? I believe a flat screw driver head.

[Tin Tin]

First check that your dipstick is the correct length - as noted above Yanmar issued a longer dipstick with revised oil levels some years ago. Second is that you likely have less than airtight top oil seal on the drive shaft between the SD 50 and the engine. It may be letting air out at a certain temperature, thus causing the oil to rise. Too much oil and it will come out too. Any leak out of oil would be obvious as it drips out the bottom of the bell housing. The top seal is affected by 1. General wear 2. Grit getting in the seal and creating a groove in the shaft allowing air/oil through, 3. overfilled oil and hence air pressure which may eventually blow the seal completely. There are U tube videos on how to replace that top seal. If there is a fine groove in the shaft this can be rectified by Yanmar approved Speedi Sleeve that fits precisely over the groove with a chrome hardened surface - tougher than the shaft. If the groove is bad, then a new shaft may be needed and expensive. Until you fix the seal and/or install a breather, keep the oil at the bottom of the dipstick marker. If it goes above top marker after operation, leave the lid off and look at it again when oil has cooled in a couple of hours. The breather system will avoid the oil passing the seal, it will unlikely alleviate the groove caused by grit, just the symptom.

[Knot Safety]

Tin tin - thanks for the great, well written and informative response. I’m guessing a seal job and a breather job are in my near future.