7.4 L Mercruiser with Water in the Oil / Tan in color

dgold_881

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May 30, 2008
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* Fresh Water Only Boat * Arizona Boat* Last season I installed a fresh rebuilt 7.4L long block 454 into my 22' 1990 Cobalt 223 due to the previous block having a crack in it. The only other item that was replaced was the oil cooler. I didn't replace the exhaust manifolds or risers.
Last season boat ran great no issues that were noticed. This year had the boat out maybe 20 mins and decided to check the engine because I heard a ticking noise. I could see the star board side valve cover was leaking the tan oil and the Riser seemed extremely hot. The boat temp was running at 150. The oil is a tan color not all the way emulsified creamy white. I was able to pump out the oil through the dip stick tube with no issues. I was thinking maybe I had a cracked manifold and water may be slightly pouring back into the cylinder causing the tan colored oil. But today after removing the riser it doesn't appear that any water was back flowing into any of the cylinders nor was the gasket from the riser to the manifold didn't appear compromised due to the perfect rust rings that were left behind after removing it also the exhaust manifold still held water. I don't want to replace just the manifold if it may be a intake gasket or head gasket. Is there a way I can test the integrity of the intake of head gaskets with out removing them to visually inspect the gasket? There is no rust in the exhaust valve area. Any help or ideas of what may be the cause or what to look for would greatly appreciated.

Darin
 
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Scott Danforth

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do a pressure test on the cooling system (I think there are directions in the stickies)
 

Lucrative

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This may be a dumb question, but did you ever get any freezing temps in your area in Arizona over the winter or was your boat stored somewhere where freezing temps occurred?

Also, where did you get your new long block from? What is the age and previous history? Is there a possibility it was compromised before you got it? Hate to ask a question that would put any kind of doubt in your mind about your new long block, but it might be something to at least consider.
 
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dgold_881

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May 30, 2008
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It gets cold but the boat was stored inside during the winter months. As far as the block I guess anything is possible, At this point I'm trying to pin point the source whatever it may be? Just hoping someone else has had similar issues before?
 

Bondo

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At this point I'm trying to pin point the source whatever it may be?

Ayuh,..... Welcome Aboard,..... Drain the motor,... Isolate the Block, from the rest of the coolin' system, 'n pressurize it with Air,....

If there's a leak, you'll Hear it,....
 

dgold_881

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May 30, 2008
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Ayuh,..... Welcome Aboard,..... Drain the motor,... Isolate the Block, from the rest of the coolin' system, 'n pressurize it with Air,....

If there's a leak, you'll Hear it,....

How do I go about doing that?
 

Scott Danforth

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I would plug off the two lines going to your exhaust manifolds. then take the line off the T-stat housing that comes from the raw water pump, insert in a plug with a bolt-in tire valve. pump up to about 30 psi
 

Bondo

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Ayuh,..... Once drained, the block drain ports are 1/4" pipe, plumb in yer air there,....
 
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