mercury motor - need help with water pressure guage

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StanTheMan0809

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Mar 17, 2010
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I have a 1988 Bass Tracker with a Mercury classic fifty (45 hp). This is the original motor. The water pressure guage has never worked, and I need to fix it. The line is disconnected from the guage, so that's my first step. I have a question though. I traced the line to the motor and found where it enters the back side of the motor block. On top of the block though, there is a threaded hole just above it. What is this????? Should there be something there? Any help would be appreciated.
 
Silvertip

Silvertip

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Re: mercury motor - need help with water pressure guage

A water pressure gauge requires that the engine end of the pressure tube be connected 1) to a "Tee" in the tell tale line or 2) to a hose barb fitting screwed into the engine block or head that has an opening into the water jacket. Water pressure then compresses air in the line which makes the gauge needle move as a Bourdon tube unwinds from the pressure. Works exactly like a speedometer.
 
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StanTheMan0809

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Re: mercury motor - need help with water pressure guage

So will it be okay if I just plug the hole in the top of the block? I don't want it to get dirt and debris in it.
 
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StanTheMan0809

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Re: mercury motor - need help with water pressure guage

The engine end of the pressure tube does not "tee" directly into the tell tale line. It goes directly into the back of the motor block. But directly above that is the threaded hole. Can I plug this one?
 
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