Changing Lower Unit Oil - Questions

[Mark Hofman]

I'm in the middle of my very first lower unit oil change. I'm surprised at how thick that stuff is. Like molasses.



I drained the unit (I couldn't quite get the motor completely vertical, but it's close) and attached the Mercury Quicksilver Pump and Gear Lube Bottle to the lower fill hole. The vent plug was laying on a paper towel nearby.



As I started to pump the gear lube in, I noticed some bubbles of air moving through the clear tube. Once the gear oil started draining out of the top vent hole, I stopped pumping. Because the stuff is so thick, it's gonna take forever for those air bubbles to work their way to the top and out the vent hole. My SEALOC manual says trapped air can cause problems. "Air displaces lubricant and can cause a lack of lubrication or a false lubricant level in the lower unit." I'm a patient guy, so I've left everything hooked up and I'll leave it that way overnight.



Here's my first question. How do I know if I've gotten all of the trapped air out of the lower unit?



And another question: Does it make that much of a difference if the outboard isn't perfectly vertical when I'm filling the lower unit? If it needs to be completely vertical, I can always put the trailer up on jackstands.



I'll check back in the morning to see what you guys suggest. As always, thanks for the help.

 

[JEFF WHITE]

ive always put the top plug in and put a few extra pumps to it.



mine does trim all the way down,but where the plugs are it drains there since they are at the lowest point of the unit.



if after you let it set for a while,you feel there might be some air in it,pull the top plug out and see.it doesnt hurt if youre not 1000% sure of it.if you see there is,put the top plug back in and remove the bottom one with the hose primed with oil and put a little extra in.

 

[Jack Long]

I have a friend that is a Mercury mech. and he said to never pump in more lube after it starts coming out the top plug, never! Later<>< <>< <>< <>< Jack

 

[Jack K]

why is that?

 

[Mark Hofman]

Okay, the job is finished. Wow is that stuff sticky.



Here's what I ended up doing. If I'm wrong and need to go back and do something else, please let me know.



I ended up putting the vent plug (top screw) back in before I went to bed last night, but I kept the bottle and pump connected to the fill hole. This morning, I put in a couple of pumps of lubricant which didn't have air bubbles in them. Then, with the system under pressure, I unscrewed the vent plug until I heard a little *puff* of air come out. Tightened the screw and pumped a couple more squirts of lube in. Waited an hour or so, and repeated the process. Got barely a *puff* out. Did it again.



Just got back from buying my wife a new stove, and when I unscrewed the vent cap, gear lube came out like it was under pressure (which it was). Quickly screwed the vent plug tight, then undid the fill hose and got the plug in with nary a loss of lube out of the bottom hole.



I don't think I have any trapped air bubbles left in the oil now. Thanks, Jeff and Bob for the help!

 

[Mark Hofman]

Would anyone be interested in me posting another Grab Bag on the topic of changing the lower unit oil? I've got pictures and EVERYTHING!

 

[Staci Matheis]

Yes!

 

[Mike Levesque]

Yes, Mofish! Just did mine for the first time about a week ago, and could use the "teachin'"...... Supposed to hold 11.5 oz in mine, and when I drained it, (for 8 hours) although it came out clean, only about 6 oz were in there!

when I refilled it, it took a little over 11.5 oz until it came out top hole. Will watch for a grab bag item on it, and to be safe I may do it over in spring if I'm not 100% sure I did it right, thanks Mo...... egMike