Frequently Asked Lower Unit (Gearcase) Questions

How often should I check my gear oil?

It's a good idea to check the gear oil every time you use the boat. In addition to checking the level, you should also check the condition of the oil. Pull the bottom plug and let a few drops run out, so you can check for water and metal shavings.

Back to Top

How often should I change my gear oil?

Once a year or every 100 hours usually covers it. Of course you should follow the intervals listed in your manual. Also be sure to use the recommended oil. Some use a standard hi-vis, some require a high-performance oil, and some electric shifts use a special blend.

It's also good to change your oil before storing it for the winter in freezing conditions, even it isn't that old. The reason for this is just to make sure there isn't any water in the oil, which could freeze and crack the gearcase.

Back to Top

Why does my gear oil look like pancake batter?

If your pancakes tasted like gear oil this morning, it was probably just a little mix-up. ;-) The more likely cause would be water in the oil. Drain the oil and pressure check the unit. If you're lucky, the problem will be something like a loose drain plug or faulty plug gasket. Otherwise, it's probably time for a reseal.

Pull the prop and make sure there's isn't any fishing line wrapped around the shaft, which can cut the prop shaft seal, letting oil out and water in.

Back to Top

How do I check my gearcase for leaks?

First, you need a pressure tester with a gauge and a fitting that will thread into one of the plug holes. Remove the plugs and let the oil drain, if you haven't already. Put one of the plugs back in and thread the tool into the other hole, then pump it up until the gauge reads about 5 psi. Let it sit for a few minutes and watch/listen for leaks.

If it holds at 5 psi, pump it up to 10. Rotate the shafts and move the shift shaft; this can sometimes reveal leaks caused by a nick, scratch, or pitting in a shaft. If the gauge doesn't hold pressure, you can usually hear the leak and find it pretty easily. If it's a slow leak, try putting a little soapy water, or other liquid, around the seal areas and watch for bubbles.

If your tool is capable of checking pressure and vacuum, repeat the above steps using vacuum. Generally, the pressure check is all you need, but occasionally back-to-back seal problems are easier to find with vacuum.

Back to Top

Under load, my gearcase sometimes clunks and jerks, almost like I hit something. Why?

Assuming that you're not hitting something, you at least need a shift cable/linkage adjustment. The problem is that if you adjust it and the problem goes away, it doesn't mean that the lower unit is fine. I'd definitely recommend a complete tear-down and inspection.

If you catch it early, the gears will probably be fine and you'll just need a clutch dog.

Back to Top

My skeg broke off, but the boat still steers fine. Do I need to replace it?

It won't affect your steering, but it might shorten the life of your propeller and/or prop shaft if you hit something else. It would probably be cheaper to replace the skeg now than it would be to repair the damage from another hit without the skeg there to take the blow.

Back to Top


Disclaimer: Use information on this page at your own risk. Seiler Marine is not responsible for the mechanical ability of others. Never attempt a repair without the proper tools and service manual. When it doubt, it's best to take it to a pro.