New Motor Getting Water in Oil

Please help!!! I just recently bought a rebuilt 350 chevy for my boat. The boat year is a 1979. Here is my only problem:

Motor starts right up and runs good. I run for about 10 minutes and by then the oil is completely milky. I have never taken this new motor on the lake and have only run it on the muffs. It has new exhaust manifolds, but didnt replace the risers. Could that much water be coming into the motor from a bad riser? Or do I have a bad rebuilt engine? Also could it be leaking from the intake? I am so frustrated considering this is a rebuilt motor and having issues like this. I just have a hard time believing that so much water could be leaking back into the motor bacause of the riser. And how do I know if it is leaking via the intake manifold. Its just hard to believe because it does run very good except for water getting into the oil. Any suggestions? Also the reason I replaced the old motor was this very same reason and thought it was cracked block. So what else could it be?

Re: New Motor Getting Water in Oil

Bad head gaskets will lose water into the oil.Also a cracked water jacket on the block or head I,m not fimilar with a marine 350 cooling system. but i do know about land based ones a lil bit.And it dont take to much water to turn the oil milky.that motor should hold about 5 quarts of oil if u really want to see how much water is in the oil drain it into gallon jugs

Re: New Motor Getting Water in Oil

Exactly what parts were reused on the new motor?
was it a "new" block or a old one reused?
not many causes for it to fill up and run good, a riser shouldnt dump that much water .might be a cracked block, bad intake manifold, intake gasket

Re: New Motor Getting Water in Oil

I assume you do not have a oil cooler.
Pull the plugs to see if you determine which cylinder(s) are getting water.
If you have a pair side by side with signs of water, it is most likely a head gasket or possibly a warped head.
If you have no signs of water in any of the cylinders it could be an intake gasket or other intake manifold issue.
I assume you have some sort of warranty?
Either way, looks like some sort of issue that should be covered.

Re: New Motor Getting Water in Oil

Ayuh,...

You can eliminate the Risers,...

If they Leak,...
With the motor Running, the water is expelled...
Only with the motor Off could they drop water into the cylinders, then the base, thru the rings...

From the description,...
I'd say either the Intake, or the heads/ block...

Re: New Motor Getting Water in Oil

Any head gasket leaks that go into the cylinders will NOT get water in the oil like you are getting. The water goes out the exhaust, not past the rings and into the oil pan. Just like leaky manifolds.
Block or intakes usually cause that big a leak. Block off the exhaust manifold water intakes and see if you can pressurize the cooling system enough to hear where the leak is.

Re: New Motor Getting Water in Oil

Was any work done to the heads?

Take off the t-stat housing off. Shine a light into the opening called the neck, see any holes thru the water jacket.

Take a screwdriver and lightly poke the wall opposite the opening.

Post here what you find.

Re: New Motor Getting Water in Oil

Well I guess I should be pulling the intake then. And it does have an oil cooler.
So when I pull off the intake what should I be looking for? I know inside the intake water jacket it was very rusty and I didnt pressurize it to look for leaks. Considering that the old engine was doing the same exact thing before I replaced it so I hope I can say its not anthing to do with the new motor. Oh one more thing I forgot to mention when I first started the motor I had my outdrive off and just sprayed water into the engine via the water hose connected to the bell housing and I hydrolocked all cylinders. I thought it was because water continued to circulate through the motor when it was shut off due to the pressure of the hose and wasnt able to leave through the riser because on the trailer the boat it isnt level it leans forward a little.

Re: New Motor Getting Water in Oil

Ok I pulled the hoses off the exhaust manifold and the exhaust manifold still was full of water so I think that can rule out bad exhaust manifold. Pulled a couple of spark plugs and noticed water droplets on the spark plug ends on all 4 I checked. Proceeded to pull the thermostat housing off and noticed water still in the intake water jacket. Its very rusty water but still had water present. Now the boat does lean forward when hooked to the trailer so I guess it still could be the intake. I guess it might not be looking for this motor. Do you all suggest pulling off the intake and check anyways?

Re: New Motor Getting Water in Oil

Ok only right side cylindes are getting water. Spark plugs on the left side were tan with no water droplets at all. So why would you only get water into one side of the engine?

Re: New Motor Getting Water in Oil

Riser, Riser joint gasketing, exhaust manifold. If any of those are leaky or bad then water can get into any cylinder on that side with the exhaust valve open as it sits.

That will not usually put water into the oil unless there is a serious cylinder sealing problem with the piston rings or pistons themselves.

I believe you have more than one issue, and the fact that the previous engine did this as well indicates many new parts are needed now.