Water in outdrive, pressure tests OK?

[nola mike]

Went about 40-50 miles last weekend for the first trip of the year, and the boat sat on a mooring for 4 days. Pulled the plug after I hauled it out, and had milky gear oil. A1G1 outdrive. I had pressure tested the drive prior to putting it on (both halves independently, and then when assembled), and it was OK. Drained the oil, pressure tested again, and again it seems to be holding pressure. Rotated the prop, no change. Usually when I've seen the leaks, the pressure is lost quickly at 15 psi. If it's a super slow leak, I can't imagine how I'll find it...any tips? In the meantime, if the weather cooperates I'm going to refill and see what happens.

 

[dubs283]

need to rotate the input shaft while shifting the drive fwd/neu/rev ensuring the propshaft is also rotating while under pressure

you are trying to fully simulate the drive in use while under pressure with this

soapy water can help, also focus on the shift shaft bushing, common place to leak. wiggle the shaft side to side and back and forth trying to get it to leak

 

[alldodge]

Lower the pressure to below 10 psi, then try 5 inHg vacuum

 

[nola mike]

Lower the pressure to below 10 psi, then try 5 inHg vacuum

How will lowering the pressure help?

 

[Bt Doctur]

Being an Alpha 1 there are few places for water to enter.
Inputshaft but then bellows would have been full of water
prop shaft
shift shaft seal
Quad seal
water pump base seal

 

[alldodge]

The shift seals are lip type. There is a spring inside to help keep pressure around the shaft. As pressure inside increases so the the pressure being applied to the lip. Lowering the pressure can help find the leak. Also see if there is any side play on the shaft, which there should not

 

[nola mike]

The shift seals are lip type. There is a spring inside to help keep pressure around the shaft. As pressure inside increases so the the pressure being applied to the lip. Lowering the pressure can help find the leak. Also see if there is any side play on the shaft, which there should not

So you're saying that the higher pressure could actually seal the leak? Not sure I get it, but pressure treated again today at 15 and 10 psi, held at both. I don't have a vacuum pump with me... No play on the prop shaft and like I said I did rotate that.

 

[alldodge]

So you're saying that the higher pressure could actually seal the leak?

Yes, if there is a bad leak any amount of pressure will leak, but a minor leak can be sealed up with more pressure

What about the vent and drain plugs, do they look ok?

 

[nola mike]

Yes, if there is a bad leak any amount of pressure will leak, but a minor leak can be sealed up with more pressure

What about the vent and drain plugs, do they look ok?

Interesting. Plugs look fine, new gaskets (and I pressure tested from both holes). Repeated at 8-9 psi, still good. Ran 50 miles today, no water on return, but the boat was only in the water for 4 hours or so. Weird.

 

[isaacs]

When you're underway, the lower unit will heat up and possibly weep some oil past the seals into the water unnoticed. When you were at the mooring, it cooled down and sucked some water in. Your last trip did not include the "cool down in the water" thing so it simply sucked in air. This is why a vacuum test would be important.

Presumably this is why Mercruiser now has an oil reservoir which will allow for expansion and contraction. You could minimize this by making sure your outdrive is completely filled with as much oil as possible. It is the air which expands and contracts.