Lower unit oil level - 3 holes

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ross_larter

Petty Officer 2nd Class
Joined
Apr 6, 2003
Messages
109
Hi,<br />On my 1996 mariner 60hp bigfoot 2/s lower unit, there is 3 screws, one at bottom to drain/fill oil, vent hole 8ish inches above it and oil check hole to right of vent screw about 1/2 inch lower.<br /><br />When i fill the unit it takes about 650ml till it comes out the oil check hole(i then put screw in oil check hole), then about another 100ml till it comes out the vent hole.<br /><br />Should it fill the oil till it comes out the oil check hole or all the way to the vent hole. My old 70hp merc only had 2 holes.<br />Cheers<br />Ross
 
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paulgp6022

Petty Officer 1st Class
Joined
Jul 27, 2002
Messages
288
Re: Lower unit oil level - 3 holes

My 2003 Mercury 75hp has the same 3 screws. I filled mine until it came out of the vent hole. The reason I did this is because there is always some oil lost when you remove the tube of oil from the drain plug because you have to play beat the clock to get that **** drain plug in quickly. By this time enough oil has leaked out to bring the level back down to the "oil level" hole.
 
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ross_larter

Petty Officer 2nd Class
Joined
Apr 6, 2003
Messages
109
Re: Lower unit oil level - 3 holes

Hi,<br />Should i fill it to the vent hole, put bottom plug back in then reopen the oil check hole to drain the oil level with the oil check hole? Does it matter if the oil is above the oil check hole.<br />Cheers<br />Ross
 
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PuddleJumper

Petty Officer 1st Class
Joined
Jun 6, 2005
Messages
314
Re: Lower unit oil level - 3 holes

I have same question posed but not completely answered in this old thread. Fill to vent or check hole? Why the extra hole?
 
WillyBWright

WillyBWright

Fleet Admiral
Joined
Dec 29, 2003
Messages
8,200
Re: Lower unit oil level - 3 holes

Fill it to the lower hole only. There are two separate chambers above the bullet, one in front of and one in back of the water intake. There is no other passage between the two and that's why there are two plugs, so each will fill fully. Filling to the upper hole would be considered overfull. That being said, I fill until it comes out of the upper. Haven't had a blown seal as a result yet and I've done hundreds if not thousands. :)
 
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