MerCruiser 5.0 Manifold Crack/Hydrolock Help

[LiquidAssets72]

Long story short, I picked up a 1989 Arriva 2050. Boat is an open bow with a 5.0 220HP Mercruiser and Alpha One. Got the boat fired up on muffs, checked for leaks etc. Got it on the water and I was letting it get up to temp and keeping an eye on it, and an old JB weld repair someone had done on the port manifold sprung a leak and re-cracked. I jumped for the key, and just as I turned the key off it puked milky oil out of the PCV breathers. Boat was running at a high-idle (900-1100RPM) when I shut it off. Looking for advice on next steps and what to look out for. I am hoping that by immediately shutting it off, and catching it quickly I am looking at pulling plugs, removing water from cylinders by cranking, and then flushing everything out very well? Should I use some sort of fluid like Marvels and coat the cylinder walls when I pull the plugs?

I found a good deal on OEM manifolds, looks like part #860246Q11. I plan on replacing both just to do it the right way. Should I replace the risers as well? I am thinking it makes sense to go ahead and buy risers as well, but curious for someone's opinion with more experience.

TIA for any help!

 

[Bondo]

I was letting it get up to temp and keeping an eye on it, and an old JB weld repair someone had done on the port manifold sprung a leak and re-cracked. I jumped for the key, and just as I turned the key off it puked milky oil out of the PCV breathers.

Ayuh,.... Welcome Aboard,...... 'bout the only way to crack cast iron is to freeze it with water in it,.....
I suggest you pressure test the block, before ya spend any money,.....
A cracked manifold will not put water into the oil,.....

 

[LiquidAssets72]

Ayuh,.... Welcome Aboard,...... 'bout the only way to crack cast iron is to freeze it with water in it,.....
I suggest you pressure test the block, before ya spend any money,.....
A cracked manifold will not put water into the oil,.....

That's what I am starting to think also, but I can't pressure test it without fixing the external crack on the manifold at least right? Should I tear it down to the heads and see if I can find anything obvious first?

 

[LiquidAssets72]

Ayuh,.... Welcome Aboard,...... 'bout the only way to crack cast iron is to freeze it with water in it,.....
I suggest you pressure test the block, before ya spend any money,.....
A cracked manifold will not put water into the oil,.....

I ordered a few gallons of cheap oil, some cheap filters, and Mercury fogging oil for now to flush it and get the cylinders coated just in case it is worth saving.

 

[Bondo]

That's what I am starting to think also, but I can't pressure test it without fixing the external crack on the manifold at least right? Should I tear it down to the heads and see if I can find anything obvious first?

Noooo,.... Then you can't pressure test it,.....

You need to isolate the block, from the rest of the coolin' system, 'n pressure test, Just the block,.....

 

[Scott Danforth]

pull the two hoses two the manifolds, pull the supply hose from the transom shield, tee them all together and pressure test.

should hold 15psi forever

 

[Lou C]

depending on where it cracked, it theoretically could put water into an exhaust port, but it would take a while for that much to show up in the oil. I agree do not take it apart, before doing air pressure testing as described above. if it holds pressure then replace the manifolds and move on. DO NOT use those old crappy exhaust parts. The are all suspect.
If it fails the air pressure test then your task is to find out where the leak is. If you are lucky it will be a head gasket or cracked head, not the block.