2002 Mercruiser 3.0 dreaded water in oil

[Phil527]

New boat owner here looking for advice:

I picked up a 2002 Starcraft with a 3.0 Mercruiser late last summer. I'll save you all the details, but last owner was not too mechanical and was selling because it did not shift into FWD. I fixed that and a number of other items, changed all the oils, plugs and fired it up for a bit and then winterized it. It started right up, sounded fine and the oil I drained I cant remember exactly how it looked, but I don't think it was real alarming - otherwise I would have been working on this over the winter.

This summer I finally get it out on the water and starter bolt snaps before I even get out of the marina!! - turns out the outer bolt was already broken and PO screwed and piece of metal to the outside instead of drilling and removing the broken piece.I was really only running on the one inside bolt.

Anyway, while I am down there I pull the dipstick and I notice my oil has signs of water!! Not a hell of a lot but devnitely is milky for oil that only has 1-2 hrs on it tops from idling in the yard and a few minutes in the water. I did a pressure check of the cooling loop on the block. Pressurized to 13PSI and it slowly drops to zero in about 3-4 minutes. I can't hear any hissing anywhere, I put Snoop/soap on my pressure test manifold, hose fittings and did not see any leaks. I want to pull the block drain valve where the blue drain hoses connect and plug those in case the valve seat is leaking.

What is a reasonable leak down rate? Should the 10-15 psi hold for an hr? 24 hrs?
How much pressure can I put in before blowing a freeze out casting plug?

My gut is telling me a cracked block would leak a bit more and would not hold pressure. This was on a cold engine, I will probably finish extracting and replacing the starter bolts, then warm up the engine and then try this pressure test on a warm block to see if there is a difference.

Other than block casting and head gasket - any other places I should look for possible paths? The intake manifold is not water cooled on these engines - correct?

Phil

 

[Scott Danforth]

you should be able to hold 15 psi for hours

no such thing as a freeze plug, however core plugs will push out at about 50 psi

how did you winterize?

only one tea spoon of water is all it takes to create milky oil

two locations for cracked block on a 3.0

first is just below the deck (head mating surface) on the manifold side
second is inside the motor along the pan rail at the bottom of the water jacket

the exhaust manifold ads 2 or 3 places for water to enter the cylinders. two places for cracks and one bolted joint that can fail.

you could always pull the exhaust manifold and inspect the exhaust ports.

dirty black from carbon is good
rusty red from water is bad.

 

[kenny nunez]

There is a very thin area in the lower water jacket on the starboard side of the engine. This is where your leak probably is located. Sometimes the leak is in one cylinders. Very rare for the cylinder head upper surface. The cheapest new replacement would be fitted block which comes with pistons, cam bearings and main bearings. If one of the cylinders is the leak do not waste your money on getting a sleeve installed.
If you shop around you may be able to find a good complete engine if there are any shops in your area.

 

[Stonefingers]

I just ran across the same issue, turned out to be a crack in the starboard exhaust manifold, water sat on top of the piston and leaked into the oil. The motor was running fine for hours on the lake, I shut it off at idle and 10 minutes later it was hydrolocked when I tried to start it again. My engine is a 5.0 MPI so a little different in some respects.

 

[Phil527]

Good to know on the small amount of water to make oil milky - maybe I am not in real bad shape. There were 2 drain cocks, one on the block and one on the lower portion of the exhaust manifold. I opened them both and let the hoses run into the bilge, they ran out freely so I don't think they were plugged. I pulled a couple of hoses off the top Tstat to make sure air was vented into the block and left it that way - I am kicking myself for not filling with anit-freeze.

I do not have any water leaking externally from the block that I have found. A little drip on the lower portion of the coupling off the exhaust riser. It sounds like it is feasible a small leak in the exhaust manifold could let residual water run back in through an open valve and down the cylinder when sitting?

I am going to double check my pressure test and take a closer look at the drain **** to make sure it is not leaking by its seat.

Another newbie question: when using the water muffs, is there a max water supply pressure from the garden hose I should be worried about?