2004 Mercruiser 3.0 Water/Oil Mix Coming Out of Breather

[CLi87]

I did a search and found some similar threads but no real answer to my issue. I have a 2004 Mercruiser 3.0 with unknown history, supposedly the boat was winterized but I'm not sure if it was done properly. When I got the boat, the oil looked good and compression test was good, on the first trip out I checked the engine bay after 10 minutes of running it at about 3k RPM's and there was brown oil all over the top of the engine, it was coming out of the breather hose that connects to the carburetor. I limped back slowly to the nearest dock and noticed spurts of water was coming out of the breather hose and there is definitely oil mixing with water. After I got the boat back I did another compression test and it still tests out good, all cylinders were about 160 psi. There was no water on the spark plugs either. At this point I'm thinking cracked block or cracked cylinder head, is there anything else that could cause these issues? I'm waiting for an adapter to arrive so I can pressure test the cooling system and see if I hear anything but meanwhile was looking to see if anyone here may have any more insight?

 

[kenny nunez]

The GM 4 cylinder engines have a thin spot in the casting in the lower water jacket that will perforate over time. Most times freeze damage is an external crack that leaks out and not in. The head is probably still good if you find a usable block.
At one time it was possible to obtain a “fitted block” that had new pistons, cam & main bearings. Then reused the crankshaft, rods and camshaft.

 

[Scott06]

I did a search and found some similar threads but no real answer to my issue. I have a 2004 Mercruiser 3.0 with unknown history, supposedly the boat was winterized but I'm not sure if it was done properly. When I got the boat, the oil looked good and compression test was good, on the first trip out I checked the engine bay after 10 minutes of running it at about 3k RPM's and there was brown oil all over the top of the engine, it was coming out of the breather hose that connects to the carburetor. I limped back slowly to the nearest dock and noticed spurts of water was coming out of the breather hose and there is definitely oil mixing with water. After I got the boat back I did another compression test and it still tests out good, all cylinders were about 160 psi. There was no water on the spark plugs either. At this point I'm thinking cracked block or cracked cylinder head, is there anything else that could cause these issues? I'm waiting for an adapter to arrive so I can pressure test the cooling system and see if I hear anything but meanwhile was looking to see if anyone here may have any more insight?

you have it right pressure test the cooling system. The symptoms you describe are that of a cracked block where cooling water enters the crankcase. You can have great compression with a cracked block like this as they rarely crack in the cylinder

As kenny mentioned usually they will crack on the outside first below the intake manifold would look down there and see if you see anything

You will see a place called center state engine advertising used bored blocks https://www.ebay.com/itm/2638052560...anIkf3gXoEH0po9I5n0u1EHxFj|tkp:Bk9SR6DW2IbXYQ

 

[CLi87]

you have it right pressure test the cooling system. The symptoms you describe are that of a cracked block where cooling water enters the crankcase. You can have great compression with a cracked block like this as they rarely crack in the cylinder

As kenny mentioned usually they will crack on the outside first below the intake manifold would look down there and see if you see anything

You will see a place called center state engine advertising used bored blocks https://www.ebay.com/itm/263805256083?hash=item3d6c04c193:g:HFUAAOSw4SxbQ2lc&amdata=enc:AQAHAAAAsM4iM+0saUhqMiNTKSQkwpOzRlifrh30ph5/Y+WWtrsxnIO8EMIh8yJgTPmilSsvmboy6W+22a3uGFg09k87x58s3/W+BILxSE66N31vWmNRqo7tgyWNItnNNtdcTj2Yt7aSM5DXeIBcn3D8arMCFl51Pz+rr8axytqvZfRyMhGDWynb6sPaR4n6VPBJxvNlNrNyxducxm5+ousachanIkf3gXoEH0po9I5n0u1EHxFj|tkp:Bk9SR6DW2IbXYQ

I did look all around the block and didn't see any cracks or rust spots from water dripping, outside of the block was extremely clean, I also checked again after having the issues but no sign of any external crack so I guess it must be internal somewhere, I get internal crack causing water to mix with oil but why would water/oil be coming out the breather hose? The spark plugs all looked clean and since compression is good I'd assume the crack isn't in one of the cylinder walls so what would cause pressure to build up like that?

 

[Scott06]

I did look all around the block and didn't see any cracks or rust spots from water dripping, outside of the block was extremely clean, I also checked again after having the issues but no sign of any external crack so I guess it must be internal somewhere, I get internal crack causing water to mix with oil but why would water/oil be coming out the breather hose? The spark plugs all looked clean and since compression is good I'd assume the crack isn't in one of the cylinder walls so what would cause pressure to build up like that?

When the entire crankcase fills up over time with milky frothy water then it comes out the breather hose. Drain the oil out if it will come out (not too gummed up)- there will be way more than 4 qts in there. If you watch the oil level you will see it rise from water entry.

I bought a boat as a handy mans special -where PO had cracked the block by not winterizing, same thing happened. The muddy milk was a pain to get out of engine compartment...

 

[kenny nunez]

The first time I encountered this one of my customers had ran the boat long enough to fill the bilge with what looked like vanilla malted milk. He told me he was determined to make it to the launch as he was fishing at the mouth of the Mississippi River and ran it all he way to the Venice marina.
The crank and cam were still good and I re used them in the new block.

 

[Scott Danforth]

I did a search and found some similar threads but no real answer to my issue. I have a 2004 Mercruiser 3.0 with unknown history, supposedly the boat was winterized

It wasn't

You have a freeze busted block or manifold