Frequently Asked Lower Unit (Gearcase) Questions
Commonly asked questions about maintaining and repairing marine gearcases. Feel free to suggest a question that you feel should be covered here.
How often should I check and change my gear oil?
How often should I change my gear oil?
Why does my gear oil look like pancake batter?
How do I check my gearcase for leaks?
My gearcase sometimes clunks
and jerks, almost like I hit something. Why?
My skeg broke off, but the boat still steers fine. Do I need to replace it?
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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.
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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.
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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.
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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, 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.
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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. It surely wouldn't hurt to replace the gears, but if you catch the
problem right away, you might be able to get away with just a clutch dog. It's not a problem you want to ignore
or put off.
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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 propshaft if you hit something else. It would probably
be cheaper to replace the skeg now, than to repair the damage that could occur if you hit something else later.
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Disclaimer: Use this information 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... take it to a shop.
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