Filling outdrive with lube

[7designs]

1973 Mercruiser 120/140 outdrive

The manual says to leave the top vent plug out and fill with lube through bottom drain plug until flows out top.

Why can't you just fill it through top vent hole until it overflows there? Wouldn't that achieve same result?What about the lube that flows out while trying to get plug back in?

Anyone do it differently?

 

[Utahboatnut]

Re: Filling outdrive with lube

Thats how I have filled EVERY drive I have ever owned, is from the bottom up otherwise air can get trapped in there giving you a false full reading. Just get the pump that screws right on to the drive lube bottle and pump it until it comes out the vent a bit, let it sit a minute and give one more pump to be sure. wipe excess off drive replace vent plug (with NEW washer) then unthread the pump fitting and quickly replace bottom drain plug (with NEW washer) and your good to go. Put an old paint tray under the drive it makes cleanup easy

 

[Diggerpine]

Re: Filling outdrive with lube

I believe if you put it in from the top, you will get an air lock and not be able to adaquately fill your outdrive. There is a method to fill it without getting an airlock.

 

[rjlipscomb]

Re: Filling outdrive with lube

Remember the gear oil is very thick and flows slowly downward via gravity and therefore has a tendency to trap air below it. Pumping it upward forces the air out through the top. The vacuum created by closing the vent and the heavy oil prevents it from flowing out the bottom when you replace the drain/fill plug.

 

[7designs]

Re: Filling outdrive with lube

I knew there was a reason. I just want to understand why I am doing stuff and not just do it. Always want to know how things work.

Thanks for the answers.

 

[ken_23434]

Re: Filling outdrive with lube

Definitely make sure the vent plug is back on before pulling the filler attachment from the bottom. As long as you don't have along delay between taking off the filler attachment and putting the plug back in, almost nothing will drip out.

 

[bruceb58]

Re: Filling outdrive with lube

Once you put the plug back in at the bottom, you can put some oil into the vent hole to replace any that may have leaked out while pulling off the pump.