Lower unit drain plug gaskets.

[Jaybord]

Are the lower unit drain plug gaskets the same size as the oil drain plug gasket? They look smaller.

[Murray]

On my engine (2009 DF90A) they are vastly different. The engine oil gasket is metal while the lower unit drain/vent gasket is a rubber washer and much smaller than the engine oil gasket.

[Jaybord]

Mine’s a 2019 DF150. They look smaller, and they’re metal. The only washers I can find online are for the oil drain.

[Murray]

https://www.boats.net/catalog/suzuki/outboard-by-year/2019/df-150apl-beginning-vin-15003p-910001/407a-gear-case

Part 15, 3 required. 1 drain and 2 vent gaskets. Interesting to note, 2 vents, only 1 vent gasket in mine. You fill from the top until oil comes out the lower vent hole???

[Jaybord]

I just remove the bottom plug and the oil level plug to drain. Not sure why Suzuki put that vent hole there,

[Jaybord]

https://www.boats.net/catalog/suzuki/outboard-by-year/2019/df-150apl-beginning-vin-15003p-910001/407a-gear-case

Part 15, 3 required. 1 drain and 2 vent gaskets. Interesting to note, 2 vents, only 1 vent gasket in mine. You fill from the top until oil comes out the lower vent hole???

thanks for that link! Ordered a bunch of stuff.

[Murray]

I just remove the bottom plug and the oil level plug to drain. Not sure why Suzuki put that vent hole there,

I’m guessing you fill from the top until oil starts to come out the oil level plug, sure would be a lot less messy than filling from the bottom until oil pours out the level plug, now you have to install two plugs with slippery oil on your hands. With an extra vent plug the drain plug could installed with clean hands, fill from the top till oil is at the level plug, wipe any oil and reinstall the two vent plug. I wish I had two vents…

[Jaybord]

No, I sill pump it up from the bottom, not sure if you can fill it from that vent hole. It is a messy process, and that gear oil has a horrible smell. After it starts coming out from the oil level hole I quickly pot the plug i and remove the pump attachment. Use lose a little oil in that process, so I let it settle over night and then check the level, if its low I slowly pump oil through that level hole until until it's dripping out.

[Harper]

I've been filling from the bottom hole, but thought about trying that vent hole up top. But now since I use Amsoil, they have a new "Easy-Pack" quart container with a very small nozzle, that you just stick in fill hole and squeeze. I'm going to try and just fill through the level hole til it drips out, just like I do with differential fluid on my vehicles. Sure makes the fill a lot easier.

I imagine that other companies probably have the same containers available.

[Murray]

What’s the purpose of an extra vent. hole? Is it higher than the oil level fill plug?

[Harper]

Yes, it's higher by several inches. I'd include a picture, but my lower unit is in the shop getting new seals right now. I really don't know its purpose, Murray. Didn't even realize that some models didn't have it. But it is marked "vent." Personally, I've never even opened it up. I've always in the past filled from the drain hole, until it dribbled out the level hole, then put the plug back in the level hole before removing the hose from the drain, so it didn't come pouring out.

[Jaybord]

How often do you guys change the lower unit oil? I change it every time I do the engine oil. I noticed that the gear oil looked like it had just come out of the bottle, no discoloration at all.

[Harper]

I do it with every oil change. Once a year. I do both by the calendar, not by engine hours.

[Murray]

I live with winter so every fall the lower unit oil gets drained not because it needs it, I’m looking for water intrusion. Engine oil is changed also in the fall, I might put 30 hours per boating season on the engine so I’ve started changing the oil filter every second year. Engine oil is fresh every fall since the engine will sit for 8-9 mouths I want clean oil when in storage.

[Harper]

I live with winter so every fall the lower unit oil gets drained not because it needs it, I’m looking for water intrusion. Engine oil is changed also in the fall, I might put 30 hours per boating season on the engine so I’ve started changing the oil filter every second year. Engine oil is fresh every fall since the engine will sit for 8-9 mouths I want clean oil when in storage.

I agree. I'm out with the boat off and on for 10 months out of the year (though I could go all 12 months down here on the gulf coast), yet seldom put much over 30 hours on the motor in any given year. I really don't like to leave the same oil in the sump for 2-3 years, even if it still has plenty of additives left. I also send in an oil sample for analysis at each change. Since an outboard doesn't run as hot as an automotive engine, the oil usually has a trace of fuel that doesn't burn off, plus I'm always aware of the possiblilty of acids building up as the oil is repeatedly heated and cooled. So the one year oil and filter change, even if excessive, gives me more peace of mind. The analysis always comes back good, and the Amsoil products I use would probably go for longer periods. It's just cheap insurance.

And this last time out, while motoring up to the ramp to recover the boat, some idiot had thrown a wad of monofilament into the harbor. It got wrapped around my prop. It came out pretty easy, and didn't appear to have damaged the propshaft seal, so I went out the next day. But I did pull the prop and look a little harder when I got home, and decided to go ahead and drain the gearbox. Yeah, there was a little water in the lower unit, so I took the lower unit in to have all three seals replaced.