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How do I check for engines damaged by forgetting to open seacocks?

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Question: I left my marina with my seacocks closed—I know what you are thinking—and, of course, after eight or nine minutes the engine alarms went off. Upon descending into the engine room, I discovered the source of the problem and opened the seacocks. The alarms stopped although I had white smoke coming from the starboard exhaust but not the port. How do I know if I’ve damaged a head gasket or something else? Both engines seem to be running fine.

— Marc Lapsley Anacortes, Washington

Professor Diesel: You need to do some visual checks as well as some maintenance. Start by looking for abnormal discoloration or peeling of paint around your cylinder heads, exhaust manifolds, engine blocks, turbochargers, and mixing elbows. Check the elbows for cracks and damage as well. Also look for burned or discolored exhaust hoses between the mixing elbows and the mufflers. Exhaust-gas temperatures under load can run 1,300°F or higher. If you find any abnormalities, contact your engine distributor or dealer and have them do a complete workup on the engine. 

If all’s well visually, change your seawater pump impellers after you’ve removed any burned-out-impeller deposits from inside the pumps. If pieces of the old impeller are missing, go through the cooling system downstream, checking the heat exchanger, oil cooler, fuel cooler, intercoolers, transmission coolers, etc. for clogs. This job is time-consuming but important. Manufacturers don’t install oversize cooling components on their engines because doing so makes maintaining and equalizing operating temperatures difficult. Any little glitch can cause overheating.

The next step is time-consuming, too. After checking and/or replacing both pressure caps and thermostats, drain and flush each cooling system and refill them with the antifreeze type your engine manufacturer suggests. Then change the oil and oil filters in each engine. An overheated cooling system means your oil’s overheated as well.

Professor Diesel is Larry Berlin, director of Mack Boring’s Training Services division.


This article originally appeared in the April 2012 issue of Power & Motoryacht magazine.