We bought an '89Bayliner Cruiser with a GM 3.0Litre OMC engine in it.
The owner told us it only needed minor repair (of course a complete ripoff!). We wound up having to purchase a used engine block because the one in the boat was broken beyond repair. My boyfriend (who is an auto mechanic and quite good with engines) took everything apart and put it back together beautifully.
We installed the engine into the boat and when turned on briefly, it purred like a kitten. Now here is where the problem comes:
When we hooked up a garden hose to the motor to get the water cooling system running, the oil mixed with the water and acquired that unhappy milkshake consistency within all of ten seconds of running time.
When we bought the used block, by boyfriend realized that somebody must have run it in salt water and not rinsed it out properly - the cooling channels were rusted like crazy.
He is now convinced that the salt water must have eaten at least a dime-sized hole somewhere into the channels, allowing the oil and water to mix so quickly. He is pretty much given up the engine as dead.
If there are other (fixable) causes for this water/oil mix that anybody knows about, please please let us know!
Any help (even advise on how that kind of leak may be fixed) would be much appreciated.

Thank you guys for your feedback and advise.
I am going to look into the bill of sale tonight to see if there is something we can do.

Im sure you know that water in oil will spin bearings and other nasty things. l wouldnt chance it with and off the shelf voodoo type repair product. Unless you can see a hole and weld it, your boyfriends correct and you need to purchase a block thats in good condition and keeps water and oil where their supposed to be.

mite be the lower unit seal leaking if not have block pressure tested if its that rusty it sounds bad

l think you will have to get yet another Block,and have it pressure
tested before rebuilding the engine,or for less work try to get a
reconditioned engine with warentee

No, your boyfriend has got it.
Go back at the guy who sold you the boat.
You will most likely have to sue him.

Unethical people make me absolutely crazy.

This type of crap ruins our sport.

Truenorth gave the right answer.go back to the person who sold u the boat & either tell him u want the money back or u will take him to court. The kicker here though is how was the Bill of Sale worded? Hopefully there is nothing in it saying ''as is.'' If not then ur b/f should have the grounds to take him to court to either recover the cost of replacing everything that needs to be replaced or getting the money spent on the boat returned to him.

Sorry to hear that this happened & realize it is a nightmare.

You might have a leaking headgasket. Just a thought. However if this waa a salt water block it may be wrecked. This is probably going to ruin the sport for you and that is too bad. Sue the S.O.B. that misrepresented the unit to you if you can. Look at the bill of sale.

Most changes r u brought the boat as is> And then changed the engine for another ur choice> Your BF might of assembled this engine with a used rusty 1> And something leaks water l have found the intake bottom cracks & leaks water into the oil gallery>Many places it could intrude> wrong head gaskets> Heads off a car>Not marine> elbow exhaust leaks>If there r plugs in the heads l have seen the leak water in the oil> If it ran good before the water then pull valve covers & turn the water on & see if there leaking> It might not be as bad as it seems>
Since it fresh water & was not ran for a long time chances r nothing was hurt just find the intrusion & change the oil & run to get the water out before any damage incur> empty the oil & turn the water on look & listen for the water leak>