Thread: Changing Oil in Lower Unit

Its that time of year again. Freezing weather is upon us, and if you have water in your lower unit, you might have a nasty surprise come spring when you decide to put the boat in the water.

The reason you would have water in your lower unit would be from a bad seal. Unfortunately, there is really no way to tell you have water in there without draining the oil and checking it for water. This should be an annual thing.

This first image shows both the upper and lower plug removed and the outboard tilted up to allow the last of the oil to drain. This is necessary on some models, and unnecessary on others.



This image is a closer view of the lower portion showing where the oil will try to drip off. Be sure to move your catch pan under here or you'll make a mess.



This is a shot of the oil that has been drained out. Notice the light area and the aura of rings around it. This is a small amount of normal emulsification. This is from water condensing out of the air in the lower unit and getting mixed with the oil. Small amounts of water are normal. Large patches of milky oil, or of completely milky oil is a bad sign.



To change the oil is simple.

With the outboard upright, place a pan under the lower unit directly below the skeg.

Remove the lower plug. A small amount of oil will start to come out.

Remove the upper plug. The oil will come out quickly now.

Once all the oil is out, pump new gear oil in through lower hole and watch for the oil to come out the upper hole. This took 100 pumps and 1/2 quart (or so) of gear oil to refill the lower unit on my Nissan 18 HP 4 stroke outboard.

Remove the line from lower hole and quickly put the plug in. A small amount of oil will leak out, but its ok. Now, replace the upper plug and clean up your mess. Yer done.

Hope this inspires you to check your lower unit and replace the oil. Check your owner's manual, or your manufacturers web site for the correct oil to use.

Yea, even though I fish all year long, I do this every winter before it turns lower than freezing temps. Better safe than sorry!

Quick Tip If You Put Upper Plug In Before Removing Bottle From Lower It Will Put Oil In A Vaccuum And It Will Not Run Out Very Fast So You Can Put Lower Plug In Easier.

What do you use to remove the plugs? I tried on my motor and they were in so tight I could not remove them. Also, what is the best oil to use?

BEWARE!!! On a lot of the older Evinrude/Johnson motors there is a phillips screw located near the vent screw. DO NOT REMOVE! This screw secures the shift forks in place and if you remove that screw there is a very good chance you will have to disassemble the lower unit to get the shift forks back in place.

Originally Posted by Ranger R61

What do you use to remove the plugs? I tried on my motor and they were in so tight I could not remove them. Also, what is the best oil to use?

I use the largest screw driver that will fit the slot and that has a square shank on it, like an older Craftsman. I push the tip in nice and tight and use an adjustable wrench to break them free. Here

is an example of the type I use.

I have had to use an impact driver

. The type you actually hit with a hammer, not the air driven type.

They usually are not that tight, but they can. If you're having trouble, tap the screw driver with a hammer a few times and see if that helps. There is a washer that is used to seal these, and that is what is giving you all the friction. Not the threads. Well, usually. If they are corroded, then a little cussing and short prayer might help.

As far as oil, I use a good brand of oil recommended by the manufacturer, or from an outboard manufacturer. Mercury makes really good oils, so does Johnson/Evinrude. I personally like Pennzoil marine products and run them most of the time.

When you replace the plugs be sue to use new gaskets. Those plugs are the most common place for water intrusion into the lower unit.

ty for the heads up and pics, as a new boat owner I'm still learning and this stuff definately helps.
Jer

Originally Posted by IBNFSHN

BEWARE!!! On a lot of the older Evinrude/Johnson motors there is a phillips screw located near the vent screw. DO NOT REMOVE! This screw secures the shift forks in place and if you remove that screw there is a very good chance you will have to disassemble the lower unit to get the shift forks back in place.

Good indicator of bad seal is an oil slick on water. This is my limited knowledge.