milky lower gear lube

[fisherman363]

I've resealed the lower unit on my 1998 25 hp Yamaha two cycle because there was evidence of water in the oil when I drained it. All seals and o-rings were replaced - upper and lower. I had a 15 lb pressure test on the lower unit while it was in a tank of water. No bubbles and the unit held 15 lbs overnight but after a hour test run in the water and another half hour in a drum the lube turned up milky again., I did another pressure test that held again overnight, I'm I missing something here?

[99yam40]

only thing I can think of is may have had water still hiding in the lower unit or you put the seals in backwards

[DennisG01]

Yeah, often a pressure test isn't very indicative of things. Truth is, it's not important if the gear oil leaks out (obviously from an eco standpoint it could be), but whether water leaks in. A vacuum test would be a better test. How were the sealing surfaces? If they're worn/grooved, that could do it, too.

[fisherman363]

Thanks for the input- Both upper and lower seals are double- back to back in the same direction with the rubber lips facing out as per the manual and that's the way the came out. Also new o-rings and one gasket. I cleaned sealing surfaces they looked ok. unit with pressure held and showed no bubbles in tank even when I rotated drive shaft and prop. I'm thinking 99yam40 idea that there may have been water left in the unit when I did repair could be the culprit but that's a long shot.

[fisherman363]

Both prop shaft and drive shaft seals are installed back to back with flat metal surface in first with rubber lips facing out, just second guessing myself.

[fairdeal]

A vacuum test would be a better test.

How does one perform a vacuum test -
meaning,
what is the pass/fail criteria?

[fisherman363]

Looks like I may have gotten some bad advice on u tube- according to service manual first seal lips face down and second seal lips face up.

[DennisG01]

How does one perform a vacuum test -
meaning,
what is the pass/fail criteria?

It's just the opposite of the pressure test. Manufacturer's seem to not want to always publish this - but the last time a Merc tech told me about this it was something like just a few pounds. He's the one that told me that Merc doesn't really care about oil leaking out - just water leaking in. Made sense to me!

[fairdeal]

Looks like I may have gotten some bad advice on u tube- according to service manual first seal lips face down and second seal lips face up.

Actual Yamaha Service Manual?
or Seloc etc?

although the application is obviously identical,
outboard manufacturers have approached it differently -
(so, IMO, there can't be a clear 'right' or 'wrong')

I've seen Mercury specify each of the two seals facing opposite

but I have never seen a Yamaha factory manual
- or parts listing -
where the orientation is "magnified" for clarity,
show anything other than this:

[DennisG01]

outboard manufacturers have approached it differently -
(so, IMO, there can't be a clear 'right' or 'wrong')

Yeah, it almost feels like it's changed over the years and then maybe even changes back... and then if it's different between manufacturers that confuses things even more.

If I remember correctly, though, the general idea is that the spring should face the thing that you want to keep out. So in this case, either both springs would face the water or the inner spring would face the oil and the outer spring would face the water. Again, though, that's if I'm remembering correctly.......

[oldmako69]

https://www.amazon.com/CTA-Tools-700...5911218&sr=8-6

I forget the values, but when I did my 225 lowers they said it should hold "X" pounds of vacuum for an hour. It did. So I then doubled "X" and let it sit for a few hours. It held. Put a smile on my face.

You can get one for less if you shop around.

[99yam40]

https://www.amazon.com/CTA-Tools-700...5911218&sr=8-6

I forget the values, but when I did my 225 lowers they said it should hold "X" pounds of vacuum for an hour. It did. So I then doubled "X" and let it sit for a few hours. It held. Put a smile on my face.

You can get one for less if you shop around.

I always thought vacuum was inches of mercury

[oldmako69]

Inches, schmintzes.....I looked at the gauge. If that was inches, you are right. I was focused on whatever "X" was.

[fairdeal]

I always thought vacuum was inches of mercury

It can be;
or as pounds per square inch (absolute)

although nowadays, outside 'Murica
neither is used;
it is expressed in "pascals" or "torr"

[fisherman363]

Seals are installed as fairdeal shows in diagram. I cleaned out lower unit after draining and found about 3 ounces of milky lube that didn't drain. Used a vacuum pump and pulled 29 inches that held for the 15 minutes I waited. I will refill and run unit assuming that the milky oil was just caused by the lube left in unit after draining. Gearcase now has passed both a pressure and vacuum test - I'll report back in a couple weeks unless someone has another idea.