SD20 Yanmar Saildrive water alarm - Questions about milky oil and secondary seal

[TwoIsBetter]

I have a new to me catamaran with 2 Yanmar 3my30s with SD20 saildrives both 4 years old.

On my SBD engine it seams the top seal when looking from the engine room is not attached in places to the saildrive metal on the interior ring. More specifically I can put my finger between the saildrive the rubber ring and touch the oil below. I assume this is not normal and will allow water to come in from the engine room. Which isn't wet often but it can happen. Of course I'll get it replaced next change to haul out.

So thats part of the background. The boat recently came off from a long passage.

First a couple of days ago we took her out and the water in saildrive alarm went off, checked the oil looked all great, tried to take out the sensor but it was stuck real well. Since I'm not really close to a mechanic I figure not to mess with it. A day later the alarm went away. I figured may be some water splashed around and got into the seal or a false alarm since those sensor are prone to that.

A few days later I was fixing the raw water intake and let a docking line drop in the water and get wrapped around the prop. In addition some water was spilled in the engine room as I was putting the raw water system back together (rem the seal that isn't totally sealed) Which caused the water alarm to go off on next start up. Fair enough either the line around the prop or the spilled water over weakened seal got in there. Checked the oil and especially the oil around the seal was dark and milky which makes sense if water floats.

So now I pumped out all the oil I could from the sail drive added new oil. Alarm is still going off. Checked the oil in the reservoir and it's clear. The oil behind the seal is much better but still has some milkiness.

So what next keep? Trust the water sensor and keep clearing out the oil and putting new oil until the alarm stops.

Is it normal that there would be some small amount of water/milky oil at the top by that seal since water floats and as long as the main oil is ok I'm good?

Something else. Advice highly appreciated.

[skipperpete]

The thin diaphragm seal on the inboard side of the Saildrive should NOT have oil between it and the main diaphragm just below it nor should it have water in that void. The thin diaphragm acts as an early warning system to alert you to problems with the main diaphragm and is not able to act as a savior in the event that the main diaphragm actually fails ( in my personal experience this has never happened but I’d welcome a first hand report from someone who has had a diaphragm failure).
The thin stainless steel band that secures the flimsy diaphragm occasionally corrodes through or otherwise releases the inner seal and it’s a bugger of a job to get the the inboard side sealed up again ESPECIALLY if it’s wet with oil.
Regarding the source of the oil that you’re seeing in the void, it could be getting pushed out the vent or dipstick seal by water entering the lower leg prop shaft seals, oil floats on water so the oil is displaced upwards. Equally, it could be the seal on the input shaft leaking oil into the flywheel housing.
I once did a test after installing one of those skinny seal retainers by attaching a short length of hose to a fitting screwed into the water alarm hole, .... at 18” of water it popped out the seal from under the clip but leaked water at the 6” mark and that was a clean dry seal and a new band.

[TwoIsBetter]

Originally Posted by skipperpete

The thin diaphragm seal on the inboard side of the Saildrive should NOT have oil between it and the main diaphragm just below it nor should it have water in that void. The thin diaphragm acts as an early warning system to alert you to problems with the main diaphragm and is not able to act as a savior in the event that the main diaphragm actually fails ( in my personal experience this has never happened but I’d welcome a first hand report from someone who has had a diaphragm failure).
The thin stainless steel band that secures the flimsy diaphragm occasionally corrodes through or otherwise releases the inner seal and it’s a bugger of a job to get the the inboard side sealed up again ESPECIALLY if it’s wet with oil.
Regarding the source of the oil that you’re seeing in the void, it could be getting pushed out the vent or dipstick seal by water entering the lower leg prop shaft seals, oil floats on water so the oil is displaced upwards. Equally, it could be the seal on the input shaft leaking oil into the flywheel housing.
I once did a test after installing one of those skinny seal retainers by attaching a short length of hose to a fitting screwed into the water alarm hole, .... at 18” of water it popped out the seal from under the clip but leaked water at the 6” mark and that was a clean dry seal and a new band.

Thanks so if the oil in the dip stick looks clear I should consider myself in the clear for now with some service to do during haul out or be worried?

[skipperpete]

Originally Posted by TwoIsBetter

Thanks so if the oil in the dip stick looks clear I should consider myself in the clear for now with some service to do during haul out or be worried?

I can’t dismiss the possibility that there’s water in the lower leg and clear oil in the top box..... highly unlikely considering this is at the end of a long delivery passage but ...maybe. if the oil lying in and around the top seal didn’t come from the dipstick seal or vent, how did it get out? Is it even gear oil that you’re seeing in the diaphragm void?
Personally, it’s my opinion that the lower leg shaft seals should be renewed at every haulout, once you know how to do the seals, it’s a fairly easy task

[ggray]

Regarding the securing of the perimeter of the top seal (I call it the top boot, so as not to confuse with the shaft seals) You can get a large, very large hose clamp and this will work, better I think than the Yanmar strap. It must be a special crimper to secure the Yanmar strap, and I've had one come apart.

But as noted above, the top boot is not all that strong.

[Tin Tin]

There seem to be two issues here:
1. Failure of the top Diaphragm retention band (There are two diaphragms that seal the sail drive to the hull, the main one is the bottom one and there is an air gap between them)
2. Milky oil in the sail drive gear box.


1. For the water alarm to go off, water has either (a) penetrated through the bottom diaphragm, which should be attended to ASAP (this may have been caused by the prop wrap or it is just plain tired (unlikely), or a previous trauma) or (b) water has entered through the unrestrained top seal + some oil from whatever source (Could be spilled engine oil, spilled gear oil, gear oil leaking from the upper drive - engine shaft oil lip-seal and it could have been there for some time. Your engine hatch might also leak rain water that could work its way in there. Any water will turn the oil that is trapped between the diaphragms, milky. So first thing to do is clean it out, use a shop wet vac or similar to suck it out through a small tube. Then reseal the upper diaphragm, heavy duty zip ties joined together may serve that purpose in the absence of anything else like a large jubilee clip, even a piece of dyneema with a loop in each end that can be joined with locking vice grips would suffice for the moment.




2. Milky oil in the sail drive gear box - this is most likely the propeller shaft seals leaking and should be replaced next haul out.

[TwoIsBetter]

Ok I appreciate the sanity check. I've had a chance to think this through and the cloud of frustration lifted a bit.

So the top seal I assume is just fine and what ever is there likely is just spilled oil - where did it come from is another mystery. It's milky also makes sense because it collects spilled water ok so taking this out.

The oil I took out from the sail drive with the oil pump generally looked clean and then I replaced about 1/3 of it (max you can get out from the oil cap side). So I'll run and check again and will assume Im ok as long as the oil is looking pretty clean. Will check seals and replace the sensor shortly.

[TwoIsBetter]

Originally Posted by Tin Tin

There seem to be two issues here:
1. Failure of the top Diaphragm retention band (There are two diaphragms that seal the sail drive to the hull, the main one is the bottom one and there is an air gap between them)
2. Milky oil in the sail drive gear box.


1. For the water alarm to go off, water has either (a) penetrated through the bottom diaphragm, which should be attended to ASAP (this may have been caused by the prop wrap or it is just plain tired (unlikely), or a previous trauma) or (b) water has entered through the unrestrained top seal + some oil from whatever source (Could be spilled engine oil, spilled gear oil, gear oil leaking from the upper drive - engine shaft oil lip-seal and it could have been there for some time. Your engine hatch might also leak rain water that could work its way in there. Any water will turn the oil that is trapped between the diaphragms, milky. So first thing to do is clean it out, use a shop wet vac or similar to suck it out through a small tube. Then reseal the upper diaphragm, heavy duty zip ties joined together may serve that purpose in the absence of anything else like a large jubilee clip, even a piece of dyneema with a loop in each end that can be joined with locking vice grips would suffice for the moment.




2. Milky oil in the sail drive gear box - this is most likely the propeller shaft seals leaking and should be replaced next haul out.

Awesome this is the sanity check and advice I needed!