Yanmar SD25 - water in oil?

[wonkywinch]

Checking the oil level in the sail drive, when opening the cap, excess oil with a small amount of "mayonnaise" flowed out. I only recently replaced the oil during lift out in May and it has been at the correct level.

During the time on the hard, I fitted a Darglow rope cutter and the running has been smooth until a few days ago there was noticeable vibration at 2200 rpm when motoring. This cleared after running astern and a quick blast of power.

I don't check the sail drive oil every day so probably 25 hours on the engine since last check when all was well.

I mopped out oil surplus and checking again after 24 hours, it looks like this (image below). No increase in level whilst sitting on pontoon without running the engine.

I guess the 2016 boat has the original seal and there is evidence of a very little black oil coming out from the side of the seal inside engine compartment. Engine has 530 hours, 250 of those in last 14 months (our ownership).

How does water get into the oil? I might suspect prop shaft seal after adding weight of rope cutter which also extended out the prop by 3cm using the supplied extension shaft.

Does a failing main seal allow water in/oil out? The drawings look like the underwater leg is bolted directly to the gearbox in the engine compartment.

Am I safe to run the engine/prop or is this a serious no go?

Based Hamble but currently in the Yealm, next stop Dartmouth where engineering help can be sought but if the boat is going to be out of the water, I prefer a return to base. Can sail but not much wind forecast this week.

Photo taken 24 hours after emulsion cleaned away.

 

[Tranona]

You are right to suspect the seals on the prop shaft. that is the only way apart from (unlikely) the drain plug for water to get it. The vibration is likely to be something round the prop that cleared after the burst in reverse. there won't be any problems with the main hull diaphragm - as you say the leg and reduction box are bolted together through that inside the boat.

The oil looks fairly clear under the bubbles so probably OK to continue motoring.

 

[wonkywinch]

Drain plug is good, I replaced the washer during my oil change. I wonder if there is a minor leak past the prop shaft that some long motoring followed by cool water allowed contraction to suck in water increasing the level and emulsifying. Of course, water is more dense so any still in the system will be sitting on top of the drain plug!

 

[VicS]

Extract a small sample of the oil with a teat pipette or small syringe. If it looks clear, with no turbidity, you are good to go. If it is not clear, i.e. milky looking, there is water getting in.

 

[Kwik Decision]

As Tranona says, failing seals on the prop shaft are the most likely cause of water in the oil. Note that in most installations, the entire sail drive unit is below the water line, which means the water pressure outside the prop shaft is at slightly higher pressure than the oil inside, thus water will leak in rather than oil leaking out. The longer you operate it like this, the more wear / damage you'll cause, particularly in the moving parts at the bottom, as they will be running in mayonnaise rather than oil. As you have noted, the more dense water will remain at the bottom, and so clear oil at the top is not necessarily an indication that all is well, particularly as something has got in there to increase the level. To fix the problem, the boat needs to be out of the water for long enough to strip down the bottom of the sail drive, remove and replace the seals (and potentially the prop shaft, if it is scored), and reassemble. It is not a job I would contemplate doing between tides.

Related to the above, I recall seeing quite a few years ago on here a mod somebody had done to their Yanmar saildrive. They fitted a header tank a couple of feet above the sail drive, such that it was above the water line. This was connected to the oil fill point with a pipe, presumably a flexi pipe, and filled with oil, increasing the pressure of the oil in the sail drive. Then, any failure of the seals at the bottom would result in oil leaking out, rather than water getting in. Not great for the environment, but buys some time before fixing the problem without causing damage.

 

[wonkywinch]

A further update, another 25 hours on the engine since and the level has not increased at all. There are still bubbles on the surface of the oil but it looks fairly clear, not cloudy.

I've ordered an oil testing kit from Millers and will run the engine/prop before pipetting off some oil for analysis. £40 was cheaper than asking a yard for their opinion and will help me make a decision.

Oil Sample Analysis

 

[vyv_cox]

A further update, another 25 hours on the engine since and the level has not increased at all. There are still bubbles on the surface of the oil but it looks fairly clear, not cloudy.

I've ordered an oil testing kit from Millers and will run the engine/prop before pipetting off some oil for analysis. £40 was cheaper than asking a yard for their opinion and will help me make a decision.

Oil Sample Analysis

You could try the 'crackle test', an ancient refinery check. Drop a blob of oil on a hot plate, a piece of steel in a mole wrench heated with a blow lamp would be a good substitute. Nowhere near red heat, about 200 C would be right. If you hear a crackle the water content is more than 2% and indicates a leak at the shaft seal. Otherwise probably not significant.

Your photo looks to me like air bubbles, not water.

 

[wonkywinch]

Thanks Vyv. I don't have a photo but it was the emulsion and increase in level that alarmed me after a check following c 20 hrs use (I know the manual says check daily but the SD filler isn't as convenient as the engine oil!).

Since monitoring, no change in level, only bubbles as pictured.

The drive is due a seal change so might have the prop shaft seals inspected when she's out of the water unless the oil analysis comes back with bad news. I don't know what water content causes oil to visibly emulsify.

 

[Halo]

I changed the bearings and seals on mine. The shaft is prone to wear and allow water in.
In my case I needed to sleeve the shaft as it had worn a lot. Google SKF speedie sleeves for details- no a hard job but you need to be out of the water. Go for the top of the range wear resistant option.
The problem is often caused by overfilling the oil. The pressure when hot drives the oil out and water gets sucked in when it gets cold.
Fill the oil so it’s just touching the bottom of the dipstick when it’s screwed up This gives space for expansion without excess pressure.
Also make sure the o ring on the filler cap is good and it’s tight. You will hear a slight his when you release it.
I make a point of only looking at the oil level when out of the water otherwise water will get in until the pressure on the inside matches pressure at the shaft ( unless you do the oil tank mod above )

 

[wonkywinch]

Thank you Halo. I remember the oil level being high when I filled it so your suggestion of expansion/contraction could be the reason.

The level is now correct as I removed some with the emulsion and has remained so.

The manual suggests a daily check with the level mid point of the stick without screwing it home (is this what you meant by screwed "up"?).

 

[Halo]

Hi Wonkywitch
I meant that I keep the level lower than recommended by setting the level with the dipstick screwed in as imho this is the lesser of two evils. I am not saying you should do this but it has worked for me for years and thousands of hours running. If you run the engine with the filler cap out and set to the lower level you will see plenty of oil being pumped round. Your call.
No sure why anyone should check the oil daily. It is at lower pressure than the outside sea water and is the lowest part of the inside of the boat. You can’t change it until she is out of the water so what are you achieving? Perhaps an occasional check to see if it’s turned to a thick emulsion

 

[wonkywinch]

Visited boat today, ran engine in neutral for 10 mins, shut down for 5 mins then checked the sail drive oil. The contents were under pressure and overflowed when I opened the cap. Doesn't look good

 

[wonkywinch]

Went back 3 hours later and it looks like this ..



Mechanically generated foam/aeration or emulsion? I'm puzzled!

 

[wonkywinch]

Good news, a Yanmar main agent's engineer visited today and took a look. Perfectly normal as he said the gearbox is known for foaming the oil. Despite the manual saying carry out a daily check, he says that isn't normal. A weekly check and only when engine is stone cold is required. Never check it when warm/just run due to the foaming issue. No mention of this in the manual but I bow to their experience.

From the horses' mouth so to speak, so peace of mind.

 

[vyv_cox]

Good news, a Yanmar main agent's engineer visited today and took a look. Perfectly normal as he said the gearbox is known for foaming the oil. Despite the manual saying carry out a daily check, he says that isn't normal. A weekly check and only when engine is stone cold is required. Never check it when warm/just run due to the foaming issue. No mention of this in the manual but I bow to their experience.

From the horses' mouth so to speak, so peace of mind.

Foaming is very often caused by incorrect base oil/additive package. If it is possible speak to one of the lubricant helpdesks. Unfortunately I have no contacts on the oil side now.

 

[wonkywinch]

I used the correct Yanmar specified/branded sail drive oil so hopefully it shouldn't be that.

 

[vyv_cox]

I used the correct Yanmar specified/branded sail drive oil so hopefully it shouldn't be that.

Yes I guessed that but it could well be that they specified it incorrectly. I have seen this happen several times with industrial equipment.

 

[Halo]

The Millers oils 80/90 multigrade I use does not froth like that

 

[wonkywinch]

I purchased an oil testing kit so yesterday ran the engine for 15 mins and then decanted the foam into the supplied 100ml bottle. This is what happened over the space of a few hours with the final picture taken this morning.

No sign of any water at the bottom of the container. I am going to contact Yanmar to see if they think the lubricating properties of their oil is adversely affected by it essentially being foam that runs over the gears, not liquid oil.

I contacted the Yanmar agent and three other engineers. Only Yanmar told me that foaming was normal for the SD25, all the engineers suggested immediate lift out for urgent attention to the seals, one said I should tow to the hoist. All saw the previous pictures I posted.

 

[VicS]

I purchased an oil testing kit so yesterday ran the engine for 15 mins and then decanted the foam into the supplied 100ml bottle. This is what happened over the space of a few hours with the final picture taken this morning.

No sign of any water at the bottom of the container. I am going to contact Yanmar to see if they think the lubricating properties of their oil is adversely affected by it essentially being foam that runs over the gears, not liquid oil.

I contacted the Yanmar agent and three other engineers. Only Yanmar told me that foaming was normal for the SD25, all the engineers suggested immediate lift out for urgent attention to the seals, one said I should tow to the hoist. All saw the previous pictures I posted.

Even after standing for 24 hours the oil has not cleared. The degree of turbidity suggests there is water present . If a sample like that had come into the lab I would have suggested a "crackle test" to confirm.

Running for only 15 minutes will not have mixed the oil completely, especially if the unit was not not in gear, and there may be free water in the lower gear case.

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