After the mess

saltysenior2

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Jan 12, 2020
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After making a stinkin' mess ,I have to ask...Why can't the gear oil be put in the top hole of the lower unit ?? 1990 9.9 Johnson..
 

racerone

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Dec 28, 2013
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Putting it in the bottom displaces the air.-----Then you know it is full when it comes out the vent.-----You can fill from the top if you add a wee bit.----wait and add a wee bit more.-----Repeat as needed till you can not add any more.
 

racerone

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Invest a few pennies and get one of those pumps.-----You screw it into the bottom.----Fill with oil.----Install vent screw.----Remove pump and install drain screw.----Loose 1 drop of oil.
 

jimmbo

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May 24, 2004
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Replacing the gasket/washer/seal on the screws is good practice, they are cheap as well
 

Vic.S

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May 4, 2004
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After making a stinkin' mess ,I have to ask...Why can't the gear oil be put in the top hole of the lower unit ?? 1990 9.9 Johnson..

Because it is almost impossible to let the air escape at the same time as you are putting oil in through such a small hole, and you cannot be sure you have properly filled it.

If you do it right you can inject the oil in through the drain hole without spilling a significant amount . Trying to put it in through the top hole makes more mess

It can be done if you have a suitable syringe, like the one illustrated but even then I find pumping in through the bottom hole is the better way
 

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saltysenior2

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one more question..if there is a leak , will the gear oil stay milkey color for a long period or will it seperate and turn dark again ??
 

racerone

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Dec 28, 2013
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Ever air mixed in will make it look milky.-------Let motor stand for some time.-----Water will separate and be at the bottom.----Oil will be dark again.-----A 1990 model may be due for new seals if it has had a lot of use.----Much cheaper than new gears and bearings.----A pressure test on the seals is a good idea.----See your local friendly boat shop for this service.
 
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