Water in the Oil +

[craig newton]

84 Mercruiser 5.7l sterndrive, 4bbl, open cooling system.
Last time out it back fired a couple times starting it and seemed normal running just above idle through the no wake zone. Once through I accelerated but didn't have enough power to plane out. Wouldn't go above 15mph. The oil dipstick showed signs of water mixed in. Removed the oil filler cap and it had white sludge all over it. Also noticed a small amount of water pooling up on the intake manifold between the distributor shaft and the valve cover gasket. I was thinking a blown head gasket and started a compression check with the #7 cylinder and it read 0 compression. Could a bad head gasket alone account for no compression

 

[Lou C]

Yes a blown HG can cause low or zero comp if it blows between 2 cyls or between a cyl & the edge of the cyl head. Your problem could be a stuck valve but water let in a cyl by a bad head gasket can cause a valve to stick open due to corrosion on the valve stem or seat. This can cause a backfire thru the intake & zero compression on that cylinder. Water pooling between the intake manifold & valve cover can be from a leaky intake gasket. Lack of power could be due water in one or more cyls causing misfiring.

 

[tank1949]

84 Mercruiser 5.7l sterndrive, 4bbl, open cooling system.
Last time out it back fired a couple times starting it and seemed normal running just above idle through the no wake zone. Once through I accelerated but didn't have enough power to plane out. Wouldn't go above 15mph. The oil dipstick showed signs of water mixed in. Removed the oil filler cap and it had white sludge all over it. Also noticed a small amount of water pooling up on the intake manifold between the distributor shaft and the valve cover gasket. I was thinking a blown head gasket and started a compression check with the #7 cylinder and it read 0 compression. Could a bad head gasket alone account for no compression

If salt water used, pitch motor. If not, tear down, at least, the #7 side.

 

[kenny nunez]

That is what it appears to be. Break out the tools. Has your engine ever had a overheating problem?

 

[Lou C]

these pix are from when I pulled the heads off my 4.3, both HGs were leaking water into the front 2 cyls and oil, if you look closely you can see a couple of valves stuck open, which might be the same problem you have.
It was cyls #1 & 2, in the bottom pic the cyl head is flipped around....top pic it is as I removed it.

 

[craig newton]

If salt water used, pitch motor. If not, tear down, at least, the #7 side.

By "pitch motor" do you mean toss it or throw it away? I mainly use this in the ocean and it has an open cooling system.

 

[craig newton]

That is what it appears to be. Break out the tools. Has your engine ever had a overheating problem?

Last year it overheated a few times. Once bad enough to melt part of the impeller and water tube. After fixing that I've had it out several times with no problems at all until now.

 

[Lou C]

I had one bad overheat back in 2013. Engine ran fine for 2 1/2 more seasons, then at the end of the third had a reluctance to start, rough running after starting and water in the oil. Pulled the spark plugs & found that there was water in cyl # 2 and just a trace of water in # 1. Pulled heads found both HGs blown, not between cyls but at the edge of the fire rings next to a water passage. Took heads to a local machine shop & they found both had cracks in the center cyls exhaust seat area & the cooling passages were eroded from 15+ years of salt water use. Cleaned up block and checked sealing surface for flatness & found it within specs (less than .003”). So bought a set of reman heads & put it back together with Fel Pro marine gaskets & new ARP head bolts. Still running well 6 years later.
A couple of overheats and yes that could have blown the HGs, however I started seeing signs of HG leaks even before that overheat…no visible water in the oil but sodium showed up in an oil analysis done 2 years before the overheating (223 ppm of sodium) .

After the repairs no water in the oil, or cyls & sodium not elevated.

 

[Scott Danforth]

By "pitch motor" do you mean toss it or throw it away? I mainly use this in the ocean and it has an open cooling system.

Have you been inspecting the manifolds every few years since you are in salt water? my guess is the manifold to elbow joint failed due to rust and you have a rusty valve in cylinder #7 and water is just pouring into the cylinder.

 

[Lou C]

The longest I ever went in salt water on an exhaust system was 6 seasons.
Any rust stains in the joint between the manifold and the elbow?

 

[tank1949]

By "pitch motor" do you mean toss it or throw it away? I mainly use this in the ocean and it has an open cooling system.

84.... Throw a way. You got plenty of usage out of it. Trust me!