# can you over fill the lower unit



## lurebreaker (Oct 11, 2008)

Hey guys, just a quick question. Is it possible to overfill the lower unit with grease? i know it sounds like a dumb question but i had to throw it out there. Thanks for any replies.


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## Michigander1 (Apr 5, 2006)

lurebreaker said:


> Hey guys, just a quick question. Is it possible to overfill the lower unit with grease? i know it sounds like a dumb question but i had to throw it out there. Thanks for any replies.


 you mean lube oil right ?


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## Burksee (Jan 15, 2003)

If your filling from the bottom (recommended way) you might be able to so on an (IO) inboard but on an outboard that would be pretty hard to do.


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## FREEPOP (Apr 11, 2002)

I seriously doubt you can, even on an I/O. There's a lot of air space in there.


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## DangerDan (Mar 10, 2005)

I overfilled my OMC stringer once. The result was a faint bearing noise. My mechanic told me 28 oz.. no more! He even shook his finger at me...:lol:

He's a cool ole guy and finding a good stringer mechanic is no cake walk. 

so,, uh,, yeah, you can.


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## FREEPOP (Apr 11, 2002)

If you fill from the bottom, as designed, I find it hard to believe but anything is possible.


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## Priority1 (Feb 5, 2006)

On the IO Mercruisers, fill from the bottom until oil runs out the open vent screw hole. There is no chance of over filling these following the correct procedure.


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## Damark Marine (Mar 26, 2008)

To answer, yes you can. I have seen guys that will pump it till the oil comes out the top which is correct, but will then put the top screw in & then give a few more pumps for "good measure". This usually causes overfilling as well as a slight pressurizing if they get that bottom screw in real fast. It tends to put alot of stress on the seals,especially the input yoke seal on stern drives. With less air space it also builds up pressure when it gets heated a bit faster which again asks alot of the seals.

Thinking of a few Merc models it also can push up water pump bases which never ends well.

Hope it helps


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## FREEPOP (Apr 11, 2002)

Priority1 said:


> On the IO Mercruisers, fill from the bottom until oil runs out the open vent screw hole. There is no chance of over filling these following the correct procedure.


That's what my experience has been.

Damark, I can see where pressurizing it would cause problems, that's what the air space is for, to control pressure for different atmospheric and temperature condiions.


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## just ducky (Aug 23, 2002)

This is actually very helpful information to me, but it also makes me question my procedure. I've always done my own lower units over the years on all of my outboards (2, 4, 6, 9.9, 15, and 50) and since I don't use a pump, here's been my SOP...with the motor in a vertical position, I take both screws out and drain the old out grease. Then for the small engines, I've laid them flat on the ground, and I squeeze new grease from the tube in through the lower hole until it starts to come out the upper hole, then I plug the upper screw, and I tilt the prop end up just slightly causing the grease to go to the upper portion. I continue to fill through the lower hole until it's backing out on me there. Then I put the lower plug in and I'm done. I've always figured that when I put it back in a vertical position, there's some air space left in the very upper portion, which I haven't considered a problem. Have I been screwing up for 25 years?


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## FREEPOP (Apr 11, 2002)

I'd say so but only the manufacturer knows if the air space is identical at both ends. IMO it is a calculated volume, at least that's what we did on the reservoirs for Mercury tilt and trim units.


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## just ducky (Aug 23, 2002)

FREEPOP said:


> I'd say so but only the manufacturer knows if the air space is identical at both ends. IMO it is a calculated volume, at least that's what we did on the reservoirs for Mercury tilt and trim units.


So if I want to do it without a pump, then what do you advise? If I do it with the motor in the vertical position, you can't get enough pressure using one of the tubes to fill from the bottom hole and watch it come out the top hole. Looking for thoughts. These are mainly small outboards...right now I have two 4's, a 6, and the 50 that's on the Lund. I get the 50 serviced at the dealer, so I don't mess with it.


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## FREEPOP (Apr 11, 2002)

I bought a plunger pump that screwed onto a quart jug (looked like a hand lotion dispenser). One trick to it is, warm the oil up. I used to put it in the sun for a few hours and that made a world of difference. You could also put it in a pail of hot water.


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