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

A boat I bought has an older V-8 stern-drive engine with a closed cooling system. What do I have to know about this kind of system and, in particular, how the heat exchanger works? P.L., via e-mail
Your closed cooling system is actually two separate systems: the raw-water system, which uses seawater, and the freshwater system, which uses coolant like your car. The freshwater loop circulates coolant inside the engine and around the exhaust manifolds, then pipes it to the heat exchanger, where heat is transferred to seawater via copper tubing. Because no seawater enters the engine, corrosion is significantly reduced, and because the coolant is thermostatically controlled--again, like your car--engine operating temperature is optimized for better combustion efficiency. The loop is also pressurized, usually to 14 psi, which raises the boiling point of the coolant, allowing for higher operating temperatures than with raw water and further increasing efficiency.

As far as maintenance is concerned, keep an eye on the raw-water system--especially zincs and exhaust elbows--as it will be susceptible to corrosion from the saltwater. Regularly check hoses and hose clamps, as well as seals and gaskets, for leakage. Inspect your seacock and raw-water pump also.

We're getting a restricted water flow from our shower due to what looks like a deposit buildup. What can we do to prevent this? B.G., via e-mail
The mineral deposits come from hard water. To eliminate it you'll have to "soften" the water--lower its pH. The best way to do this on a boat is by installing a cartridge filter designed for this purpose. This is a relatively easy job, and by following the instructions supplied with any of the units on the market, you should be able to do it yourself.

You can remove the residue by spraying the shower head with a product such as Tilex, then scrubbing it with a toothbrush. If the buildup is particularly heavy, remove the shower head and give it a more thorough cleaning inside and out with the cleaning product. If you have a chrome shower head, try soaking it overnight in a plastic bag filled with vinegar. A thorough cleaning the next day with freshwater should do the trick. If you have a brass or brass-plated fixture, do not use vinegar on it, as this will ruin the finish. Keep at it with the Tilex-type cleaning product. 

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