5.7 mercruiser hydrolocked

[Rockinw]

My 1990 Mercruiser 5.7 hydrolocked after being used this summer for 10-15 hours. There was about 2 quarts of water in the pan and when I pulled the spark plugs, water ran out of the rear two cylinders on the starboard side. I pulled a compression check and found low compression on these two cylinders. Removed the head, did a visual check, no obvious cracks, replaced the head gasket and did a new compression check. Compression was back up to specs. Ran the engine for 10 minutes, pan again had bulk water, about a quart, and there was again water in the rear two starboard cylinders. I visually inspected the exhaust manifold, no obvious signs of cracks, no water tracks in the soot. I also ran water through it with no signs of leakage. My question is where to go from here? Is the block toast? The engine has good compression and runs well, but water is getting in, large amounts in a short time.

The engine is 7 years old, a Jasper long block rebuild, and is raw water cooled, with about 250 hours on it. The exhaust manifolds (GLM) have one season on them.

I'm thinking probable freeze damage, though why did it take so long to show up? The engine has a Marine Science Technology Guardian flush system that I have used for years to winterized the motor by flushing antifreeze through the engine.

Are there any tests that can be performed to determine where the water is getting in?

 

[mkast]

Re: 5.7 mercruiser hydrolocked

Pressurize the block.

 

[hard-3]

Re: 5.7 mercruiser hydrolocked

remove water circulator pump and thermostat housing. make some blank plates to block of the water inlet and outlets and pressure test with compressed air. if there is a crack that is that large you will hear air leaks. if it is a small crack in cylinder or head it may not show up unless the engine heats up

 

[Mn Warrior]

Re: 5.7 mercruiser hydrolocked

Did you have the heads checked for cracks, or JUST a visual inspection? You may have a crack in one head or it could need to be straightened (resurfaced). Check the old head gasket to see if you can tell where water was passing by. You could also pressure the cylinders with shop air to see if it air leaks into the other cylinder, the cooling system, or crankcase.

 

[bolo78910]

Re: 5.7 mercruiser hydrolocked

how old is the manifold/risers?? just looking at them sometimes will not show much, if they are old just replace them. good luck.

 

[Don S]

Re: 5.7 mercruiser hydrolocked

Manifolds/risers will not put a lot of water into the oil when running, matter of fact no water gets into the oil from the manifolds and risers even if they do leak as long as the engine is running. Only when the engine stops, water leaks into the manifolds and leaks thru any open valves. But it usually doesn't run past the rings, just sets there till you try to start and then you have your hydrolock.
For water to be getting into the oil in bulk, you have a cracked block or a head gasket or intake manifold gasket leaking directly to an oil passage.

 

[Rockinw]

Re: 5.7 mercruiser hydrolocked

Thanks for all the replys, the prognosis doesn't look good. The manifolds were only one year old and I replaced the head gasket and intake manifold gaskets when I had it apart and thought it was only a blown head gasket. Looks like its new long block for me.

 

[nimrod69]

Re: 5.7 mercruiser hydrolocked

I had that happen to me. Water would leak into the cylinder at high speed and bog down the engine. The culprit was GLM risers/manifolds. They have a history of poor quality and leaks. Check them carefully.