Fresh vs Saltwater

Fresh vs. Saltwater Cooling

by Conrad & Judy Kreuter

Q: Dear Boat Talk: How efficient is a fresh water cooling system as opposed to a raw-water cooling system in terms of engine life, replacement of manifolds, risers, etc.? I use my boat about 50 to 60 hours per season. Also, do engine flushes work to reduce salt and corrosion? AB, Smithtown, NY.

A: Dear AB: A freshwater or closed cooling system, uses permanent anti-freeze and fresh water mixture (in a 50-50 ratio) to keep the engine block at the proper operating temperature. The coolant flow through this closed system includes the engine block, water circulation pump, thermostat, exhaust manifolds, and the heat exchanger. Raw or seawater still circulates through the seawater pickup, into the sea water circulation pump, through the heat exchanger, into the risers, and finally out the exhaust.

The benefits of a closed cooling system are well known. A large section of the cooling system is protected from the corrosive effects of salt water, thereby extending the life of these components. You can expect to have about double the life for these components.

The risers are located on top of the exhaust manifolds and connect to the exhaust collector at the stern of the boat. These curved metal tubes are generally the first components to succumb to the effects of salt water. Clogging occurs at the curve or bend in the riser and is the cause of replacement. In the fresh water system, salt water is introduced into the riser after the bend.

You can add a fresh water cooling system to your salt-water cooled engine. Kits are available from the engine manufacturer for this retrofit and typically cost around two thousand dollars plus installation. If your boat is a current model, the engine is equipped with high tech materials to combat the effects of salt water.

Your closed cooling system will still require regular maintenance. Every second year, the antifreeze should be drained and refilled. The heat exchanger should also be opened and cleaned at this time as well. If your boat is a newer model, check your owners manual for coolant replacement as some manufacturers have begun using anti-freeze which does not require changing for a longer period of time.

Regular flushing of the raw water cooling system will help to keep the effects of salt water to a minimum. Some owners have installed quick and easy flush out systems using a few hoses and plumbing fittings, so that after every use this can easily be done. Other use flushettes or earmuffs, which need to be used on land since they are impractical to use in the water. At the very least, you should flush the raw water system of your engine at the end of each season.