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.