1987 Mercruiser 2.5L 153cid mcm120 LOTS of water in oil pan

bunky2004

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May 22, 2016
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So Im a newbie here and to boating in general. I have seen this question posted a few times and cant seem to get the information I need from the other posts. My situation is as follows; A week ago I bought my first boat. It is a 17 ft 1987 Crestliner Nordic with a 2.5 Mercruiser 2.5 in it and an OMC Cobra outdrive. Previous owner stated that the boat was winterized prior to storage outside under a cover for the winter. When I first brought the boat home, I was prepping to start for first time (checked oil (which looked good) muffs and garden hose) and had no power to my dash. Found problem to be faulty alternator. Removed and replaced, power issue solved. Then I went to try to start again and started was stuck. Removed started, disassembled, cleaned, and reassembled and problem was solved. After turning on garden hose and a few cranks she popped off. Ran pretty good actually. Sputtered a few times but then smoothed out and all was well, I was ready for field testing. Today I went to change the oil and filter and upon removal of the drain plug A LOT of water came out before any milkshake came out. Now, Im an auto mechanic for a living so I know that milkshakes mean water forcibly mixed with oil. That being said, this is where I need help. I know that marine engines are substantially different but am unsure as to what makes them different. In addition to that, I have no idea where to begin for diagnosis. Are there any known issues with these engines and or weaknesses that seem to be common for water intrusion? Any and all suggestions would be greatly appreciated.

Mike
 

Bondo

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Previous owner stated that the boat was winterized prior to storage outside under a cover for the winter.

Ayuh,..... Welcome Aboard,..... I think you were lied too,..... Ya got a cracked block,....

Drain the block's water passages, block it off, 'n pressurize with air, 'bout 15 psi, 'n Listen,....

Follow the hissin' sound to the cracks,....
 

bunky2004

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May 22, 2016
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29
Where should I block it off and pressurize at? I was looking at the hoses at the thermostat housing but not sure which ones to mess with. Also if the block is cracked is there a decent substitute that will bolt in? I don't need much more power then what would be in this motor. Being a newbie to the boating world I don't know that a big engine with a lot of power would be a good idea
 
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Bt Doctur

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Aug 29, 2004
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19,425
remove the T housing, remove the oil pan drain plug, fill block and see if it runs out the drain plug
 

Scott Danforth

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pretty sure your block is toast

I would start looking for a 3.0 motor to replace your 2.5 liter
 

Fishermark

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Oct 19, 2003
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pretty sure your block is toast

I would start looking for a 3.0 motor to replace your 2.5 liter


I would agree with that route. If it turns out you need a new engine, (and it sounds like you do), then the basic 3 liter would be an easy swap. It will give you a little more power than the 2.5. There are a lot of 3 liters out there so you should be able to find a used one at a reasonable cost.
 

bunky2004

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May 22, 2016
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29
Well honestly I think this might be a case of me being stupid. So I have run 5 oil changes through it and it is completely clean now. The tech at the local marina said that its not uncommon for water to seep into the engine through the carb over winter especially if the boat is left uncovered (it has a cover but if water pools on the cover it will drip through). When I tried to start I forced the water and oil to mix....thus milkshake. Block pressure tested ok :) Today I finally got to do my long awaited field test and encountered a new problem. The engine seems to run about 140 degrees on the muffs but when I put the boat in the water it overheated rather quickly. I pulled the line off the thermostat housing from the manifold to make sure that my impeller was pushing water to the thermostat and I effectively soaked the inside of my boat. So I know that I have water coming to the thermostat but I don't seem to have any circulation. In the automotive world, I would suspect a water pump right away and of course a thermostat. With this being a marine engine (which I seem to know nothing about) I am a bit hesitant on what to do next. Any thoughts? (maybe need to start a new topic?)
 
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