Oil leaking from raw water intake?

Question

2002 crownline 185br 4.3l mercruiser, 94hours

Backed my boat down on a hill today for about an hour while i had new gravel laid on my property. After i put the boat back, i was tightening up the cover when i noticed an oil leak from boths sides of the raw water intake on the lower unit.

When i winterized the boat last fall, i cracked open the lower (fill) plug just to make sure no water came out, and got nothing but clean oil (I change all fluids mid spring)

What seals could have gone bad there? There is no water intrusion as i drained it all today and the oil looked fine.. Any help would be great

-Jess

Answer 1

Did you keep the lower unit filled with gear oil all winter, or did you drain it?  I can't tell by how you said you cracked it open, then you said you changed it mid spring.  You are supposed to change the gear oil in the lower unit before you winterize it, the whole reason is to get any water or moisture out of there, and fill with fresh oil.  Even a little moisture or water can freeze up and crack or expand gaskets.

Answer 2

Disregarding the answer above that appears to have no idea what a Mercruiser unit is, I would ask what did you use to prevent corrosion in the water system when you winterised?

Some people use anti-freeze, I personally use a water soluble coolant, same as used on lathes etc.

The only thing I can think of is that you are getting a leak from the upper part of the outdrive leg ( there is a seal on the vertical shaft that runs into the water pump housing).

The upper housing seals do have a tendancy to fail after a couple of years, especially if you do speeds that get the boat up on the plane and expose more of the upper part of the leg.

The leg gets quite hot with the exhaust passing through it, and when the boat comes off the plane and settles back in the water, the sudden cooling creates a partial vacuum in the upper leg housing and then cause it to overpressure next time you plane. Oil will then leak past the seal and run down the vertical shaft and out through the water intake.

You won't see this when you are running because the water takes the small spill away.

I take it you have a Bravo leg fitted, these ( and the Alphas too) should be pressure checked on a full service to ensure seal integrity.

I have just had a complete leg rebuild on my boat, as on the service (and water pump renewal) it was found that the upper housing was almost completely full of water with resulting ruined bearings.

So was it result of the winterising, or the possiblity of a failing upper housing seal?

Answer 3

It is possible it is motor oil that was trapped in cylinder some how and gravity let it pool. I have had this happen on a 4 stroke outboard. Smell the oil to know if it is motor or lower oil.