More of this Feature • Part 1: Heat Exchanger Operation, and more • Part 2: Oil Oxidation, and more
Related Resources • Maintenance Q&A Index

I've inherited a 40-hp outboard. What points on the drive unit should I check as part of a regular maintenance schedule? K.T., via e-mail
While there are only four checkpoints, they are all important. First, check the level of the lower-unit lube oil. In most drive units this means unscrewing a plug with a screwdriver and making sure that either oil dribbles out or you can feel it with your finger. Be careful, as there are usually two plugs; check the upper one as the lower one is for draining only.

At the same time note the color of the lube oil. If it's cloudy, you've got a leak, probably around the prop seal. Have this fixed immediately. When replacing the screw, make sure it's seated properly and in tight.

Next, check the condition of the zincs you can't see, especially the one inside the lower unit in front of the prop. You also may have a large zinc brick up under the transom bracket. As long as each is intact, you're still protected. However, if one of your zincs is at least half-worn since you checked it last, this is a sure sign you've got a corrosion problem somewhere.

Third, look for nicks and scrapes on the drive unit, and touch up any with the paint recommended by your engine manufacturer. If not, you will be inviting corrosion problems.

And last, regularly check for leakage around the trim cylinders, loose parts or wires, and any kind of obvious damage.

What are some tips for preventing epoxy resin from running or sagging? W.R., via e-mail
There are usually two possible causes. The first is applying the epoxy too thickly. You can prevent this by using #800 roller covers to roll out the coating into a thinner film. In addition, warming the epoxy with a heat gun set at low temperature before applying it will also thin it out.

The second is too slow a cure. Make sure the ambient temperature you are working in is warm--72°F is ideal. If you are working in cold weather, between 40 and 50ºF, warm the resin and hardener before mixing them to speed the cure. Or you can use a faster hardener. Check with your manufacturer's instructions for mixing and application and always follow them carefully.

What is meant by oil oxidation in a diesel engine? G.D., via e-mail
Oxidation occurs when any substance or element--be it metal or oil--combines with oxygen. The result can be rusted metal or degraded oil that loses its ability to lubricate. Oxidation is a natural and inevitable process that can be accelerated in oil by the presence of certain combustion byproducts and certain temperature and humidity conditions. Oxidized oil loses its viscosity and contains organic acids. In the extreme it can plug filters and leave deposits on rings, pistons, and cylinder walls.

Lube oils are formulated with additive packages to control, but not eliminate, oxidation. Choose oil with the proper rating and weight, and change it regularly as the additives wear out. If you have any questions about this, refer to your engine reference book or contact your engine manufacturer.

Need help with a maintenance problem? Write to Maintenance Q & A, Power & Motoryacht, 260 Madison Ave., 8th Fl., New York, NY 10016. Fax: (917) 256-2282. e-mail: ken_kreisler@primediamags.com. No phone calls, please.

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