Cracked exhaust manifold = milky oil

[Stacraft1768]

Hey guys I am in need of some opinions here. This spring I started my boat up, and it ran great, i ran it for about a half and hour on the muffs, all while watching the temp gauge. Ran great, I then shut it off and left it for a few hours. That afternoon I came back and the darn thing was hydro locked, won't turn over at all, I pulled the valve cover and discovered milky oil...I assumed the worst. I took the motor out and disassembled it, and found that deep inside the exhaust passage of the second cylinder there was a dime sized piece of casting that had broke off exposing a water jacket. Can this be the cause of the milky oil? I have thourghly searched this block and head for signs of cracking and have found nothing. I removed the Pistons to check the cylinders they look great although the rings were pretty washed out and rusty. I am days from beginning the "fingers crossed" rering and assembly, I would like to get opinions. I haven't ruled out the head and head gasket but I will take it to a shop to get pressure checked and decked. Also the rod bearing and mains are checked and plastigauged.

 

[alldodge]

If there is a hole thru to the water jacket, sure water can come in there. Is this the spot your talking about?



Now if you have batwing style exhaust manifolds, these have caused many issues with hydrolock and water intrusion. This is for 4.3 but same style for V8

 

[Stacraft1768]

Yes that's it, I have a 3.0 omc, thanks for the quick response. I have spent a lot of time wrenching on hot rods and this motor I beautiful on the inside, just wanted to make sure that I wasn't over looking something else. by chance or good luck I shut this motor down before anymore damage

 

[Stacraft1768]

Reassembly will begin soon, anyone else have thoughts on this?

 

[jimmbo]

Where was this 'dime sized' hole. in the cylinder head or the exhaust manifold? Either could explain the hydro lock, but I find it harder to believe that caused the water in the crankcase

 

[HT32BSX115]

I have thourghly searched this block and head for signs of cracking and have found nothing.

Did you pressure check the block?

The most reliable way to pressure check a marine engine is to isolate the block and head connect a gage and your air compressor and pump it up to about 15 psi. If it holds pressure, it's not cracked.

Cracked exhaust manifolds usually do not allow enough water into the oil to make it milky.

 

[Stacraft1768]

Took the head in it was cracked.

 

[alldodge]

Bummer, but sure beats the block