Mercruiser 4.3 Water in Oil

[AMMO DAWG]

If you may have seen my previous post I was trying to resolve a timing cover oil leak on my 4.3. I took the expert advice from this forum and bought a GM OEM cover (much heavier than China aftermarket) and it addressed the leak, however when I checked the dip stick I had milky oil. I was running the engine out of the boat since I was trying to make sure I fixed the leak. This is a new rebuild by a reputable machine shop, new internal components, water pump, thermostat, gaskets and new manifolds and risers. So I started looking for the source of water in the oil and started with the manifolds. Sealed the top where the riser attaches and filled the exhaust ports with water. Then I pressurized the lower water port to 25psi. Both held for 20 minutes with no bubbles in the water, no air escaping from the water jacket to the exhaust side. Next I pulled the intake manifold and pressurized it, no problem there. I'm going to pressurize test the cylinders next to check for head gasket or a crack in a cylinder wall. There was no water in the block over the winter so I know winter freeze cracks are not the issue. Not to mention we never had a hard freeze this winter in NW Florida. My question is if the block was leaning a little nose down when I ran it can water run back down the exhaust through the riser. I did turn the water on for a bit before starting the engine to fill the block and make sure it ran out the riser. I also stuck a couple pieces of PVC pipes in the rubber boot in the riser to direct the water/exhaust away from the engine. It's a head scratcher, any past experience, theory's or advice is greatly appreciated.

 

[Scott Danforth]

Florida had its share of hard freezes, even as far south as Sarasota and Bradenton. The panhandle had freezing weather this winter

drain your cooling system and pressurize the cooling jacket. it should hold 15 psi forever. if it does, its not coming in thru the cooling system.

acetone test the manifolds (take them off the engine, fill them with acetone. if there is a small crack, water may not go thru unless the manifold is warm, however acetone will flow thru quickly.

additionally, where is your timing? if you run too far advanced timing, you can suck in exhaust and water

 

[Scott06]

Agreed you want to pressure test cooling system with intake on it. Could be a leaking intake gasket at water crossover. Maybe head bolts that go into water jacket ?
wondering if break in lube used during assembly might be cloudying up the oil, or did u change it already? Either way would buy several gallons of rotella and a couple filters, change the oil as you are working through this

 

[AMMO DAWG]

Here is the pressure test I did on both manifolds

 

[Rick Stephens]

Very first thing to pressure test is the block itself. Plug everything else off and pressure test it. Need to reinstall the intake.