Drive lube refilling question (Bravo III)

MDboater

I started pumping lube in through the lower drain/fill hole with the upper hole open and reservoir cap loose.  With about 2 quarts of lube in I saw lube draining out through the upper hole.  So I screwed in the upper plug and continued filling.  With about 2 3/4 quarts of lube in I noticed the reservoir filled to the lower line.  I gave it 2-3 more pumps and checked again and saw that the reservoir was filled to the correct operational level.   So I closed the reservoir cap, unscrewed the pump tube from the fill hole, and screwed in the plug.  Some lube drained out while I screwed in the plug so I checked the reservoir to see if I would need to add any and discovered the reservoir full to the very top.  The lube level had continued to rise even after I stopped pumping and let some drain out.  So I unscrewed the upper plug and heard a release of air (like there was a pressurized air pocket). 

I thought that filling from the bottom was supposed to prevent air pockets.  My guess is that the thick lube on a cold day somehow formed a pressurized air pocket.  The pressurized air continued to force lube into the reservoir after I stopped pumping.  Has anyone experienced anything like this? 

Thanks,
MDboater

Dream_Inn

I pump until I see it come into the reservoir, just like you did.  My guess would be maybe before you switched quarts, you pumped some air in?  Either way, I think you'll be fine doing what you did.  Filling from the bottom until it's in the reservoir is correct.  The lube will also settle down a bit, so you probably didn't need to take any out.  I can't say I've experienced what you did, but the 'settle down' part, may be just what you had.

SeaHare

i alway just fill until lube comes out the vent hole, then close it all up and top off the monitor resivoir.... ive never heard of anyone pumping lube past the vent hole

Michael T

@MDboater, agree that some air got pumped in. Watch it carefully in the Spring as your drive will likely "burp" some air and drop its level, after just a few rpms - quite common.

checkmate

Why can't one just drain lower end and refill from reservoir?   I realize that it may take awhile for gravity to take effect.   Maybe a stupid question but just curious.

Michael T

@Checkmate, imo not a stupid question at all. To be honest I can't think of a good reason except that you might risk not properly filling the drive as the gear lube is quite thick - even when warm - and, it might take a long time to run through? Therefore, my friends and I have always filled via the lower drain hole, plugged the upper hole then back filled from the reservoir. Maybe your suggestion is better?

BTW - after doing this we are careful to monitor the gear lube reservoir in the Spring as these drives often "burp" air and then the gear lube level will drop.

rasbury

That is the way Merc says to do it...had an alpha II and it was the same...does really not make sense totally but, I tend to follow the mfg. on things like this...

MarkB

I would think it's because air rises.  By filling in the lower end up you are easily displacing the air in the drive as you go, all the way up to the reservoir.  If you go the other way around you need pressure to work that air out, as it will tend to rise opposite the direction you want the lube to go in, and you basically do not have enough pressure via gravity to overcome this resistance, especially given the viscosity of the drive fluid.

It's the same reason why you need the engine running to work out those last few air bubbles, that are literally suspended in the thick gear lube.