Water in Oil... part 2 ...(5.7 Mercruiser)

sillydilly

Seaman
Joined
Sep 10, 2012
Messages
62
hi all. I've posted here a few times about an engine swap but I'm still having problems.

RECAP.
bought a boat with a cracked 5.7 2bbl Mercruiser. Bought a good truck engine off a family member and did the swap. Came with block and heads complete and never taken apart. everything else was marine (I did swap
out cam). Ran fine in driveway for an hour at operating temp. I took it for a test run on the water and within 5 minutes I had water in the oil. I cannot pinpoint where it came from.


INTAKE MANIFOLD
first suspect. had this magnaflux tested and it came back okay. Though it was out 0.002 and 0.003 in some places, machinist said its fine to use but at the edge of "do I mill it flat"? So intake seems fine

EXHAUST MANIFOLDS
although usually a problem after sitting - I checked the exhaust manifolds by capping off at the riser and sealing the water jackets from exhaust. applied 20 PSI at the drain valve and dipped it under water. no bubbles at all came out of the exhaust or anything after 20 minutes

EXHAUST FLAPPER
known to fail and suck up water during a fast trailer launch, or sudden decel and engine kill. I only stuck my hand down the pipe and felt both were intact, springy, squishy, uncracked and damaged. will
follow up with a boroscope check to be sure.

CRACKED BLOCK
although highly unlikely, this block came out of a good running mechanic owned truck that didn't use oil or antifreeze.




What are some other suspectable culprits I can look into? head gasket ?


Thanks ! (I look forward to bondos advice 😋)!
 

sillydilly

Seaman
Joined
Sep 10, 2012
Messages
62
I figured it would be easier to collaborate whats been going on in one clear updated post without having to go through all the replies and previous troubleshooting. I'm also on mobile and it's very difficult to maneuver the forums.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,306
The truck block should have had the core plugs changed to brass and the head gaskets changed to marine (stainless)

How much water did you find in the oil? Are you running an oil cooler?

Did you use the correct intake manifold gaskets?
 

sillydilly

Seaman
Joined
Sep 10, 2012
Messages
62
Scott I didn't find a whole lot, the level
on the dipstick was significantly higher and the oil was milky. No I'm not running an inner cooler

I used truck intake gaskets
 

bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,454
I looked through your other thread just now. I suggested in the second post if you pressure tested the block so not sure if you did that or not. Did you do that?

BTW...people have to now go back to your other thread to see all that you did or didn't do so now we have to look at two threads. That is why you don't start a second thread on the same issue.
 

sillydilly

Seaman
Joined
Sep 10, 2012
Messages
62
gave each hole a squirt of 2 stroke oil for a compression test. 150+ on all holes except 2&4.

got about 100psi.

both holes next to each other with lower compression suggests the head gasket must be leaking


pressure test??? working on a system right now to plug all ports and apply pressure. does anyone have any good suggestions ?? with the hardware stores closed I just siliconed a few sockets in the outlets and seems to be working well. waiting on some
silicone to cure on the inlet and I'll see if it will hold 15lbs

what have others used to help pressure test block? if it is a head gasket how can I find out where ?


thanks !
 

sillydilly

Seaman
Joined
Sep 10, 2012
Messages
62
No Title

just bout ready to apply some air.. had a few hiccups from a leaky socket plug. going to go 10psi and see if it holds

just need silicone to cure
 

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bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,454
On some of those, the easiest thing to do is take the hose that comes off one side and loop it back to the other side.
 
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