Foamy Gear Oil

[Mirage Gecko]

I have Yanmar 3ym20s coupled with the Kanzaki ZD 20s sail drives.Checking the drive oil today one is perfect but the other has about 1mm of foam on top.You can remove the foam with paper towel and the oil is clear and smells normal also the level appears correct.No abnormal traits while motoring forward or in reverse.
Does the presence of foam always indicate water or possibly something else?
Chris

[belizesailor]

Water doesn't usually foam, just emulsifies (mixes w oil and turns a creamy/brown color). I would change as much oil as you can (vaccum pump out thru fill), top up, and see if it happens again.

You do mean foam, like dish soap foamy, right?

[Mirage Gecko]

Yes describe it as foam but heavier than dish soap closer to the crema on a good short black coffee not really like an emulsion.I will see what I can rig up to change the oil.
Chris

[belizesailor]

If the drive was sitting unused long enough for the water to start to come out of emulsion then it will form a cream like layer at the surface. Maybe something caused it to look a bit foamy (not sure what that would be).

Letting the water come out of emulsion and sit for an extended time is when damage gets done. I've seen boats in the charter fleet with shaft seal leaks which were in regular charter use, so the water was mostly kept in emulsion, oil changed (pumped out so not 100%) in between charters, and sent back out on charter with no immediate ill effect (not ideal long term of course). Seals changed when charter schedule permitted.

[Khagan1227]

Another couple of sources of oil in foam:

Oil level is too high

Anti-foaming additives in the oil are gone, usually as a result of age of the oil or the oil has been foaming for a while and used the anti-foaming additives up.

[belizesailor]

Now that you mention it, I have seen them foam on overfill.

[AliaVita]

I know this is a very old thread, but did the OP arrive at any conclusion? I have just hauled and replaced both seals on both sail drives of my catamaran. Routine maintenance, not because of a leak. New oil in both drives, obviously, but immediately the starboard lube is frothing. Definitely NOT water. Aerated is the way I would describe it. After 20 minutes standing it disappears and the lube looks perfect. I can only think that something in the reassembly on one side is causing this aeration as it wasn’t there before, or the oil was bad, or..........

[Bad Dog]

I too have foaming oil in my SD20 saildrives, recently hauled out, new seals & oil & also it clears up after 20 mins sitting idle. I used a Penrite oil to specs.
photo didnt attach. light green small bubbles.

Maybe too full? The old oil did the same.
Some oil people say its normal as long as it is less than 15% of the total oil in the drive.

[Bad Dog]

Yep spoke to a guy who worked in the mining industry running gearboxes and says it is very normal while spinning as the oil aerates and is always foamy while running 24/7 with no problems. it settles when stopped but his gearboxes rarely stop.


I now only check the level when cool.