Filter Management Page 2

Maintenance Q & A — April 2001
Maintenance Q & A — April 2001
By Capt. Ken Kreisler

Filter Management

Part 2: Clogged relief port, and more.

 More of this Feature
• Part 1: Filter Management
• Part 2: Clogged relief port, and more
 Related Resources
• Maintenance Q & A Index
• Maintenance Editorial

Can my outboard be damaged if its relief port becomes submerged? M.J., via e-mail

Yes. The most common result of a clogged relief port is “coking,” the buildup of carbon deposits. This can lead to knocking, pre-ignition, and poor fuel and oil management. Left unchecked, these problems could lead to piston damage and engine failure. A discussion of what happens to exhaust gases during outboard engine operation may help explain why.

All cylinders dump exhaust into a common manifold where water is introduced to cool and muffle it. The exhaust-water mixture then passes down a passage in the drive unit and eventually exits through the propeller hub. When a boat is at idle or slow speeds, however, the static water around the prop produces too much resistance to the exhaust, resulting in excessive backpressure. (When the boat is moving, a low-pressure area behind the propeller prevents this.) To alleviate this problem, one or more passages are cast or machined into the intermediate housing just above the waterline. If pressure builds at the prop, the exhaust can escape through these ports. If these ports are restricted—say, by overloading the boat to the point where they are submerged—exhaust won’t escape, cylinder temperatures and pressure will rise, and deposits will form.

I tried to fix a small hole in my inflatable but found that the patch would not hold, even when I tried several different glues. What could be wrong? B.F.L., via e-mail

You probably used a silicone-based compound like Armor-All to clean your inflatable. The chemicals in it infused the fabric and the glue therefore could not adhere to it.

To correct this problem, you’ll need to clean the area with a strong solvent and may have to sand it as well to ensure a good bond. Contact your boat’s manufacturer for solvent recommendations. How can I remove masking tape from stainless steel fittings? H.R., via e-mail Lacquer thinner or nail-polish remover will do the job. Brush the liquid on so that it coats the tape. Let it soften for a while. You should then be able to carefully peel off the tape. If any adhesive remains, rub the area vigorously with a thinner-damped rag. Use lacquer thinner and nail-polish remover with caution, as both will attack varnish, paint, and many sealants.

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: No phone calls, please.

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This article originally appeared in the May 2003 issue of Power & Motoryacht magazine.

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