More of this Feature • Part 1: Lift-type Muffler, Engine Noise • Part 2: Galvanic Corrosion, Misfiring Outboard, and more
Related Resources • Maintenance Q&A Index

While checking the oil on my stern drive’s engine, I noticed what appears to be sludge on the dipstick. What is going on, and what can I do about it? C.B., via e-mail
Your oil may be contaminated or simply have been in the engine too long. (Hopefully you have been doing your scheduled oil changes as specified by your engine manufacturer.) Drain the oil immediately, refill with the proper oil, and change the filter. You may want to send the old oil out for analysis to determine the cause of the problem.

If the problem recurs within the specified change interval, you may have a more serious problem, including a cracked head or block or defective cylinder head gasket.

How does galvanic corrosion occur in a diesel engine’s cooling system? V.S., via e-mail
It’s caused by electrical current produced by the different metals that make up the interior components of your engine and flows through the coolant. In raw-water-cooled engines, sacrificial rods or zinc pencils are designed to absorb the current flow, so these must be checked regularly for deterioration and replaced when almost half is gone.

But that’s not the only way galvanic corrosion can occur here. It also can be the result of an exterior source. To help prevent this type of situation, the electrical system must be designed so that all grounds are tight and free from corrosion. Some of the more common trouble spots are improperly grounded electrical components and a corroded ground strap connection. Regular checks and cleaning will eliminate any potential problems.

Aluminum parts of newer engines are more susceptible to electrolytic corrosion–the metal requires only about one-half the electrical potential as iron to produce the same damaging effect–so owners of such engines need to be more watchful of this problem.

My carbureted outboard engine has begun to misfire at idle. What should I check? C.A., via e-mail
Begin with the spark plugs. They may have the incorrect gap, be fouled, or be otherwise defective. Fouling is sometimes the result of an incorrect spark plug heat range. Incorrect ignition timing is another possible culprit.

Also check all spark plug wires for corrosion or poor contact and the condition of your coil and points and condenser if so equipped.

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: kkreisler@primediasi.com. No phone calls, please.

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