HELP! 1988 4.3 omc had water in the oil.

[UPTHERIVER]

Hello all.
I have a 1988 OMC 4.3. I had just replaced the motor. Prior to removing it from the donor boat it test ran it for over a hour. And it ran great. No issues other than the exhaust manifold did have a crack, and was leaking into the bilge area. The oil looked fine. ( freshly changed at the start)
Now I installed it in my boat, and lake tested it for 20 minutes. And I have over a quart of water in the oil.
I replaced the exhaust manifolds with the ones off my other motor that were good.
The only difference between. The engines is my old one was a 2 barrel, and the replacement engine is a 4 barrel.
That should not matter correct?
They looked the same. Other than the markings. Old ones say 4.3 liter. Replacement engines said 4.3L 4 valve on the manifolds.
I did a pressure test on the engine cooling system and it slowly leaks down.
We did a leakdown test of each cylinder and all passed.
What are your thoughts?

 

[88 Capri (2022 SOTY)]

Hello all.
I have a 1988 OMC 4.3. I had just replaced the motor. Prior to removing it from the donor boat it test ran it for over a hour. And it ran great. No issues other than the exhaust manifold did have a crack, and was leaking into the bilge area. The oil looked fine. ( freshly changed at the start)
Now I installed it in my boat, and lake tested it for 20 minutes. And I have over a quart of water in the oil.
I replaced the exhaust manifolds with the ones off my other motor that were good.
The only difference between. The engines is my old one was a 2 barrel, and the replacement engine is a 4 barrel.
That should not matter correct?
They looked the same. Other than the markings. Old ones say 4.3 liter. Replacement engines said 4.3L 4 valve on the manifolds.
I did a pressure test on the engine cooling system and it slowly leaks down.
We did a leakdown test of each cylinder and all passed.
What are your thoughts?

Hi there.
Well water in the oil means there could be a crack in the block somewhere and I only say this because of the results from the cooling system leak down test and exhaust manifold cracks which could be from improper winterizing. When you said the oil was fine in the replacement engine, do you mean like just changed?
This is the first thought that came to mind.

 

[Scott Danforth]

Buy new manifolds. If there is a crack on the outside, there are cracks on the inside

If your pressure drops on the cooling system test, you have a crack in the system somewhere. It should hold 15 psi forever

 

[Bondo]

I did a pressure test on the engine cooling system and it slowly leaks down.

Ayuh,.... Welcome Aboard,...... Sounds like yer replacement motor has the same problem the original motor had,......

 

[Lou C]

The exhaust manifold having a crack, suggests that the past owner didn't drain it, and if one thing is cracked (as easy as those manifold drains are to get at) then other things are likely to be cracked.
Personally I don't have the patience at all for fooling around with other people's old Junk. If I need a new engine, it will be a rebuilt from a local machine shop with a warrantee. I simply can't see wasting time with other people's junk, life is too short.