Merc 5.7 Water in Oil

[jtrasap]

Okay, so this is my first boat. I bought it as a project at a very good price and even if I end up having to repower it I'll be ahead, but, I would definitely like to expend my options before going that route. The boat had a cracked exhaust manifold and milky oil when I bought it so I was ready for the worst(cracked heads/block). I replaced both exhaust manifolds and changed the oil, ran it and still have a water leak somewhere so I pulled the intake manifold and found milky oil in one of the intake runners but none in the corresponding intake port on the head or any of the head ports for that matter so I changed the intake gaskets thinking maybe it was just a leaky intake gasket but after reassembling and running it still has a leak. My next step was to pull the heads and check for cracks in the heads and block and look for leaky spots in the gaskets. I just started on that job and again when I pulled the intake manifold I have milky oil in the same intake runner but none in the corresponding port on the head. It just seems strange to me that this would be the only place that would have milky oil. Maybe cracked intake? I still don't get why the milky oil would be in that one runner and none be in the head as I would think that it would get sucked in there by the vaccuum?

 

[Th3Skipper]

Re: Merc 5.7 Water in Oil

Have you tried a compression check? Also did the intake have any rotting?

 

[Don S]

Re: Merc 5.7 Water in Oil

Post some pictures.

How much over full is the oil level on the dipstick.

 

[jtrasap]

Re: Merc 5.7 Water in Oil

Checked compression and they all look good. The manifold is in pretty good shape as well. After changing the intake gaskets and letting it run this morning for about 20 min I ended up with about a half quart extra. I took some pics earlier, I'll post them when I get to the house this evening.

 

[Don S]

Re: Merc 5.7 Water in Oil

Checked compression and they all look good. The manifold is in pretty good shape as well. After changing the intake gaskets and letting it run this morning for about 20 min I ended up with about a half quart extra. I took some pics earlier, I'll post them when I get to the house this evening.

You have either a cracked block or the water passage on the intake manifold is cracked or rotted through.
Since the manifolds were cracked, I would bet the block is too. Pull the intake and look for cracks behind the pushrods, and check the underside of the intake manifold under the water passage.

 

[Bondo]

Re: Merc 5.7 Water in Oil

Checked compression and they all look good. The manifold is in pretty good shape as well. After changing the intake gaskets and letting it run this morning for about 20 min I ended up with about a half quart extra. I took some pics earlier, I'll post them when I get to the house this evening.

Ayuh,.... Welcome Aboard,... You bought a motor that's been Frozen, Fulla Water,...

there's No salvage there,... Long block it, 'n move on,...

When ya take it apart, ya loose the ability to pressure test it to find the leaks,...
Is it together Now,..??

If so, Drain it, block off the coolin' jacket, 'n pressure test it with air, 'bout 10/ 15 psi,...
You Hear the leaks, listen through the "Holes" ya got to work with, oil fill, spark plug holes, carb, exhaust ports, etc...
The bottom of the intake, the lifter valley, 'n the inside of the oil base, opposite the water drain plugs are all candidates,...

 

[jtrasap]

Re: Merc 5.7 Water in Oil

Okay, now that I'm home and actually looking at it, the manifold does look a little rough. inside the water passages.





This is what's got me a bit stumped, the milkshake is making its way into the number 6 intake runner. This is the only place other than the obvious places that oil normally travels in the engine. It's not in any of the the intake ports on the head including the nuber 6 port that matches right up to the milky intake runner. I keep coming back to the intake due to the milky runner.

 

[Don S]

Re: Merc 5.7 Water in Oil

Looks more like an old OMC than a Mercruiser, but it's still a 5.7, and there is enough milky oil and rust on the engine side of the intake to tell me you have serious problems. Do you have milky oil coming out the vent hoses into the flame arrestor when running?

Post some pictures of the lifter valley on both sides and the bottom of the intake. Not just a close up of a single port.

 

[jtrasap]

Re: Merc 5.7 Water in Oil

It's an 89 Mercruiser 5.7 alpha one. The exhaust manifolds were more a case of being rusted out rather than cracked, the stern side was rusted through and by the looks of it the port side would have followed suit shortly. No milky oil coming out the crankcase vents.

these are the best pics I have at the moment, I'll get some better ones tomorrow.

 

[Idlespeedonly]

Re: Merc 5.7 Water in Oil

It looks like the block is newer than 89, since it is setup for a roller cam.

 

[jtrasap]

Re: Merc 5.7 Water in Oil

Most gm blocks from 87 on up were drilled for roller cams but they didn't start using them in the trucks until 96.

 

[jtrasap]

Re: Merc 5.7 Water in Oil

Okay got the head torn off of the side that had the milkshake in it and it's pretty clear now what happened and there is no way that my buddy could have checked the compression on all of the cylinders. I pulled the head and found water in numbers 6 and 8 and number 6 piston was beat to crap by chunks of the valve seat. So, I'm guessing the leaky manifold caused an overheat on that side, causing the head gasket leak and the dropped valve seat. Without that valve seat that cylinder had no compression allowing the vacuum from the other cylinders to suck the water from that cylinder. which is why only that runner on the intake had signs of milkyness. My guess is that the head surface was hot enough to burn it off so it didn't appear in them.

 

[jtrasap]

Re: Merc 5.7 Water in Oil

A little update: Block block was magnafluxed, bored .030 over, and the decks cleaned up. Got some new used heads, port matched and polished, weiand intake, Holley carb and extreme marine cam. Getting ready to go back together.