That buildup will cause a couple of bad things to happen. Think of it as cholesterol plaque in your cooling system. Left unattended, this stuff will eventually form a coating inside the comparatively small passages inside your heat exchanger. Things like micro-organisms, calcium, and lime are still getting by the strainer and are indeed going to leave deposits inside the raw/seawater side of your cooling system. No matter how sophisticated your raw-water strainer is, understand that it was only designed to keep weed and other relatively large debris from entering your cooling system and clogging the raw-water pump. Today these shops are going the way of starter and alternator rebuilding shops, into extinction due to economic and environmental reasons, so letвЂ™s rule that option out.ДЄ raw-water strainer is the first line of defense itвЂ™s only meant to keep out relatively large debris. Back in the day, it wasnвЂ™t uncommon to remove the heat exchanger every couple of years and send it off to the local automotive radiator repair shop to get it acid-dipped and boiled out thoroughly to clean out all the deposits.

This raw-water side of your cooling system is where annual maintenance is critical. The seawater then gets pumped overboard, usually via your engineвЂ™s exhaust system (there are closed-system variations on this system in the commercial and large-vessel worlds, but weвЂ™ll leave those for another article). This seawater gets pumped through the heat exchanger on your engine and, via convection, pulls the heat away from the tubes inside the exchanger. The marine-unique issue So, unlike automotive applications where air is the primary element in extracting heat from the engine, in marine applications we count on seawater (or lake water, or river water) to do the job. Obviously, the best bet is to follow your engine manufacturerвЂ™s recommendations on maintaining the closed side of your engineвЂ™s cooling system. However, some engine-makers recommend changing out the coolant every two years. This is comparable to Mercury MarineвЂ™s five-year or 1000-hour extended-life coolant for Mercury engines. Prestone, for example, touts its product as being good for five years or 150,000 miles in automotive applications. Combine all those requirements and you can begin to see that modern engine coolant is a robust but complicated fluid. And the coolant itself must have an extended service life. Engine coolant must be engineered to inhibit corrosion of internal engine passages, and neutralize acids and other byproducts of combustion. Those deposits need to be flushed out regularly-once a season is best. Inside the raw-water side of the heat exchanger, calcium-lime deposits will build up and reduce engine-cooling. Increased pressurization and advanced engine metallurgy have driven the folks who design and make what today must be referred to as engine coolant versus mere вЂњantifreezeвЂќ to come up with some very sophisticated chemical formulas. For every pound of pressure added, approximately 3В° F can be added to your engineвЂ™s operating temperature, improving its thermal efficiency.

By increasing the pressure inside the closed part of the system, the boiling point of the coolant is enhanced. These systems are pressurized, just like your car or truck. Today almost all new marine engines use the closed cooling system design. It is undoubtedly getting much better mileage than its 15-year-old counterpart. Consider a modern automobile that will typically run at 215В° F. ThatвЂ™s when you know itвЂ™s running at peak efficiency, assuming proper fuel and exhaust system design. The trick with any engine is to get it running as hot as it can run without causing any damage. The cooler temperatures also caused varnish and gum buildup inside the engine, which ultimately contributed to other problems. This comparatively cool running temperature limited the engineвЂ™s ability to reach a maximum level of thermal efficiency, which in turn had a negative impact on fuel economy and to some degree overall engine longevity. This was done to minimize the possibility that salt in the salt water would separate out and crystallize inside the engineвЂ™s cooling passages, with 160вЏ being the critical turning point for this to occur. They had a thermostat, just like all engines, but it was regulated at 145-150В° F. Besides exposure to corrosive materials in the water, raw-water cooled engines suffered from another major drawback. A cutaway view of this heat exchanger shows cooling tubes, expansion tank, pressure cap, and sacrificial zinc anode on the lower right.

Inboard engine