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Discussion Starter · #1 ·
Headed out to the Chesapeake Sunday to troll for rockfish (caught two keepers) and on the way back the ingine sounded like it caught a bag. I stopped and looked at the prop, no bag. It ran like it had no power. I noticed gray white grease or oil build up on the exhaust ports just below the head and at the exhaust port at the prop. I idled into the dock and went home. Last night I pulled the plugs and they were very dirty. I then checked compression in each cylinder, 130, 125, 130 and 130 PSI. Compression seems fine for a 1974 Mercury 50. I cleaned the plugs and put them back in the engine and it started fine, idled and ran at high rpms fine. I then decided to check the lower unit oil which looks to have been polluted. It is gray white like the oil coming out of the exhaust ports. I dropped the lower unit and will work on that tonight. I will drain the oil, take apart the water pump, remove the prop and during all this look for a bad seal. I was wondering if it is possible for lower unit oil to enter the compression cycle. When I pulled the plugs they were dirty but no signs of any water or oil foul, only normal black buildup from years of use so I do not think the water and oil is getting into the heads. Not to mention the compression test shows no signs of any gasket or head cracks. Anyone have any idea what is going on here? Things to look for? Thanks for your help.
 

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Discussion Starter · #2 ·
I wanted to list a little history. Took the boat to the ocean last fall, brought it back and she sat until last weekend. Had 3 gallons of fuel in her from last year. I have an 18 gallon tank. It sits outside with a cover on her. Exposed to the heat and cold etc. Could I have gotton water in the fuel? Could the salt water eaten at my lower unit seals?
 

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Judging from my sterndrive it would be waterpump seals. Replace seals and impeller and whatever needs to be and it will solve most of your problems. Many machanics are saying replace waterpump every year or 2.
Bill
 

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The plug issue may be from water in your fuel and you have or had a fouled plug. I would replace them and check to see if you have water in your gas. The best way is to disconnect your gas line and pump some gas into a jar. The water will sink to the bottom and if you do have water add a separator. fouled plugs could be why you notice the oil around the exaust area because its unburned gas and oil. The lower unit is probably a totaly different issue. On most lower units you have three places where water can enter the unit. One is the shaft for the prop and the other is the shaft that runs to the motor. The third would be the seals around the shifting rod. Your best bet is to change all three because the repair bill on the lower units can get very expensive. The loss of power was probably the fould plug or plugs.
 

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The milky color is definitely water mixed with gear lube. Most likely a bad seal. There are usually two shaft seals. They fit back to back and have to be installed a in a certain direction. Output shaft seal and shifter seal can give the same problem. My money would be on the drive shaft seals. Overhauling the water pump would be a good idea while it is apart. If you do it yourself check out the shafts and make the are not scored. This can happen with a bad seal.

Good luck
 
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