Water in engine...looking for help

[djaymasa]

We had a beautifully running early 90s merc 5.0 that we just replaced all the pistons, gaskets and carb. It ran really well for the first 7 hours of breaking in and then a spark plug popped out of its socket. We stopped the engine and installed new spark plugs.

Ran the boat for 30 minutes and we found chocolate milk.

We tore apart the motor and all gaskets are fine, the intake is fine and the heads are fine. We've looked over the block and still don't see any issues either.

The manifold has a decent crack in it now and was not there before we took it out. Pic attached. We filled the hoses attached to the manifold with water to see if any droplets came out and nothing after 2 days. So we're just not sure...

Is that all that could be the problem is the manifold? Any other ideas?

 

[Scott Danforth]

pressure test the motor's water jacket. it should hold 15 psi

that manifold looks like it may have froze. at a minimum, you need new exhaust manifolds.

 

[Bondo]

Ayuh,..... Unfortunately, I'm guessing that motor froze before you did all yer repair work, 'n you missed finding where the block is cracked,.....

What's the back-story on this motor,..?? Why were you swapping out the pistons,..??

 

[Lou C]

Yep if the gaskets look good that is the most likely cause is a freeze up. What is odd though is that the manifold has that crack yet there does not seem to be a sign of water in the exhaust ports, no rust there….

 

[djaymasa]

Ok so it's a VERY long story....

Original and actual boat is 1990 180 horizon. Had a 4.3 omc in it. That motor was cracked. We found a 89 invader with 5.0 merc in decent condition but the hull was horrible.

We spent last year changing everything over to merc. We replaced a few things like gaskets, oil and other things. We had to fabricate an extended mounting setup for it but it works. We were able to take it out a few times before the end of summer last year. We noticed it ran oddly after a couple hours, struggled to get to speed and hold, but never got water in the oil.

We took the entire engine apart and found 2 pistons completely destroyed and decided to go for new. Obviously that was a decent answer. We didn't notice ANY other damage what so ever...
We had the engine apart until last month once we got the rebuild parts so there's no way it froze as it was completely apart and stored in our garage.

And going off Lous response with no rust in the ports. This would make sense if the crack just happened on our last outing 4 days ago.

I can't seem to think that a spark plug blowing out would cause this reaction and crack the manifold but could it really???

 

[Lou C]

Well that’s a mystery for sure…I had water in the oil some years back and that was due to an overheat a few years earlier. Too bad you took it apart already! Is this a pre Vortec or a Vortec engine (12 bolt or 8 bolt intake?) Vortec engines were known for bad intake gaskets which were upgraded later on…and those can cause water to get in the oil for sure…

 

[djaymasa]

12 bolt intake, so what are you saying for the upgrade?

 

[Lou C]

If you have a 12 bolt intake it’s a pre Vortec which was not known for failing intake gaskets & water leaks into the cam valley & oil
The 8 bolt (Vortec) was known for failing intake gaskets
The change was in 1996 IIRC. Vortec heads have about 25 more HP.
If you have the 12 bolt the intake gaskets aren’t a likely cause of water in the engine oil.

 

[djaymasa]

Thank you for the info. We'll see about a pressure test.

One thing I failed to mention earlier is the oil pressure gauge was reading fairly high at all times. Usually around 60-70.

We couldn't figure out any reason why that would be. Could that cause issues?