Mercruiser Lower Unit Reservoir Level Falling

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capdan

Recruit
Joined
Sep 7, 2010
Messages
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2002 5.7L Alpha Mercruiser (250 hp). Just had lower unit oil changed by dealer. No indication of problem from dealer, but since I've had the boat back, the Reservoir oil level is falling. There is no evidence of oil on the outside of the lower unit, in the bilge, on the reservoir or hoses or in the exhaust (through the prop). I checked the fluid and it is green and clear (no water). The leak is happening while the boat is sitting on a lift (not running). Where else could the fluid be going???
 
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dubs283

Vice Admiral
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Jul 27, 2005
Messages
5,096
Re: Mercruiser Lower Unit Reservoir Level Falling

often when changing the fluid, air pockets develop and it is normal to see a drop in the resivior bottle

also, some of the lube in the monitor system may have drained out with the old lube and they didn't top off the resivior bottle

fill the bottle to the full line and keep an eye on it for the next few runs in the boat, it will probably level off and maintain
 
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capdan

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Sep 7, 2010
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Re: Mercruiser Lower Unit Reservoir Level Falling

Thanks dubs, I have topped it off twice, but have not run the boat since. If the weather cooperates maybe I'll take it out tomorrow and check it again when I get back. I've read about those bubbles, is it possible that it would take multiple topping off and/or running to work all of those out??
 
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capdan

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Sep 7, 2010
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Re: Mercruiser Lower Unit Reservoir Level Falling

I guess I should have clarified this a little further. When I got the boat back from the dealer after he changed the lower unit, I noticed he did not tighten the fill/drain set screw completely. It was leaking a small amount of oil. I tightened it myself and filled the reservior (it was empty). Since then, the level in the reservoir has fallen a bit. I have topped it off twice but it has still fallen. Was I wrong to try to fill it from the reservoir or should I have filled it from the fill/drain set screw.
 
Alpheus

Alpheus

Lieutenant Commander
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Aug 3, 2009
Messages
1,757
Re: Mercruiser Lower Unit Reservoir Level Falling

Put a pump with your oil in the bottom fill hole and take the vent screw out of the top. Pinch off your reservoir line and slowly pump some oil into the bottom. Even if a little oil starts coming out of the top give it another pump or two just to bleed any air pockets out. Put your vent plug back in followed by the fill plug. Un-pinch your reservoir line and fill the reservoir to the full line.
 
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