Water in my mercury 40hp gear case

Wolf84

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May 28, 2013
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My Outboard is a Mercury 1997 40hp and serial is 0G465268

Recently, i flush my gear case oil and i found water in. I have change my prop shafts seals, fill with new oil and run the engine on muff.

After running above 10 minutes, the gear case oil is white again.

My questions :

1 - If water go in gear case when the engine run on the muff, the leak is probably the water pump base seals or shift shaft seal ???

2 - If the water pump base seal is bad, the gear case oil go up in water pump or the water go in gear case or twice ?

Thx and sorry for my bad english.... is not my first language.
 

GA_Boater

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Re: Water in my mercury 40hp gear case

Welcome Wolf. Water getting into the lower unit on muffs is most likely the water pump seals. As the impeller rotates there are high and low pressure areas, so water can be forced into the lower unit by the higher water pressure and the oil is forced out of the housing into to the pump and sent through the motor. I hope that makes sense.

Can you do a pressure and vacuum test on the lower unit? That will pinpoint where it's leaking. If you can't test it, just replace all the water pump seals, gaskets and impeller. Good luck.
 

Wolf84

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Re: Water in my mercury 40hp gear case

Thx for reply !

I read some post on the web above the gear case air pressure test but i'am not sure to have the equipment for... can i do this test with compressor only or i need special tool ?

For the seal, do you think that the shifter seal can be the problem too or only the water pump seal ?
 

JB

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Re: Water in my mercury 40hp gear case

Did you replace the gaskets under the Vent and Drain/Fill plugs? Failure to use new gaskets every time is a common cause of water intrusion.
 

Wolf84

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Re: Water in my mercury 40hp gear case

ok ....but if the problem was the screw washers, I don't think that 10 minutes on the muff is enough for water intrusion by the screw ?
 

JB

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Re: Water in my mercury 40hp gear case

Those are plugs, not screws and the parts under them are gaskets, not washers. I take it you did reuse them, Wolf.

You asked for advice. That is my advice, no charge.

EDIT: I notice that Merc calls them screws and washers. My apology. Yes, water can get in there in 10 minutes. Always use new gaskets. . . .um. . . washers. :)
 

Laddies

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Re: Water in my mercury 40hp gear case

If your running on muffs your problem is definitely the seals at the bottom of the water pump, while your at it you might just as well change the impeller and the shift shaft seal. remember when removing the shift shaft seal to not let the shaft raise and come out of the shift cam on the bottom.
 

GA_Boater

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Re: Water in my mercury 40hp gear case

JB and Laddies both have good advice. I was going to say go ahead a replace the shift shaft seals also.

The vent and drain screw seals do cause a lot of water in lower unit problems. I don't know if it shows up running on muffs, but a good habit is to change them anytime you remove the screws. Good luck with this, Wolf.
 
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