Monthly maintenance: diesel engine coolant

Coolant was once always green, but now comes in multiple colors.
Steve D’Antonio

Antifreeze is an essential component of any liquid-cooled internal combustion engine that relies on a closed cooling system. It should be called “coolant” because it does more than prevent freezing.

In a closed cooling system, excess heat created by the engine is absorbed by the coolant and transferred, via a heat exchanger, to seawater and pumped overboard with the exhaust gases. From the 1930s to the 1990s, almost all of the coolant used in applications like this was the well-known green ethylene glycol (called IAT, or inorganic acid technology), which provided protection against corrosion and corrosion. lubricated the circulation pump, offered freeze prevention to about minus 30 degrees Fahrenheit when mixed at a 50-50 ratio with water, and raised the boiling point to about 15 degrees Fahrenheit above that of plain water. Pressurized cooling systems, like those in all modern diesel engines, also increase the boiling point; at 15 psi, the boiling point of ordinary water is 250 degrees Fahrenheit.

Today things are different, mainly in the area of ​​choice; There is a range of coolants to choose from, including Organic Acid Technology (OAT), Hybrid Organic Acid Technology (HOAT), and Nitrided Organic Acid (NOAT) Technology, as well as some proprietary coolants designed for specific engines. These formulations provide engines with better corrosion protection and longer coolant life. Then there is the color: In addition to green, there is blue, pink, orange and red, and while these colors may indicate a particular chemistry, this is not a guarantee.

Always follow the coolant instructions provided by your engine manufacturer, and never add coolant without knowing what is already there. In an emergency, it’s better to add water (preferably distilled, but anything will do in a crisis) than the wrong coolant. The main job of the coolant is to prevent freezing, but if that’s not a problem, the water will work just fine in the short term.

tube bundle
The coolant surrounds the outside of the “tube bundle” of a heat exchanger; if overheated, a film may deposit on them, which can prevent heat transfer.
Steve D’Antonio

When changing coolant, whether it is a similar or a different chemical, plan to flush the system to remove sediment and all traces of old coolant. Remember that conventional ethylene glycol is poisonous, so do not leave uncovered containers outside where they can be accessed by pets or children, and always clean up spills (it evaporates very slowly) and dispose of old coolant properly.

If you have decided to replace your coolant, you should do it again according to the engine manufacturer’s guidelines, and in the absence of these, approximately every 1000 hours or three years. Unless the manufacturer specifies one of the more modern varieties mentioned above, most sail aids and generator sets can use conventional IAT; however, it must be formulated for use on a diesel engine.

Diesel engines, especially those that rely on a “wet” cylinder – in which the outer wall of each engine-cylinder liner is in direct contact with coolant – can experience a phenomenon known as water erosion. cavitation, sometimes called oscillation. With each stroke of power, the cylinder inflates slightly and then quickly contracts, creating a void or cavitation bubble that violently implodes and, in doing so, pulls metal out of the liner. This all happens on a microscopic basis and takes time for damage to occur, but after enough time it can lead to cylinder liner leakage and failure. It’s rare on sailboat auxiliaries, but why risk it? By using a high quality diesel coolant (these include anti-cavitation additives) and changing it regularly, you will virtually eliminate this possibility. Additional anti-cavitation additives are also available, and these can be added on an annual or hourly basis.

corrosion inhibitors
Since engine blocks are usually cast iron, the coolant should include corrosion inhibitors (as well as cavitation inhibitors).
Steve D’Antonio

If you are using a concentrate (that is, a coolant that requires the addition of water rather than a preformulated liquid), be sure to mix only with distilled water. Do not use tap or bottled water. Water containing minerals can leave scale deposits in the cooling system, preventing heat transfer. Unless otherwise specified by the manufacturer, the mixing ratio should be 50-50 for the best balance of corrosion protection, freezing and boiling, as well as heat transfer (pure distilled water can transfer more than heat than coolant, which is why it is undesirable to increase the coolant-to-water ratio beyond 50 percent). Anything less than a 30% coolant ratio can allow biological growth to form in the cooling system, especially on engines that are infrequently used. So stick to the 50-50 ratio for the best results.

RELATED: Sailboat Diesel Engine Analysis

Finally, if you’ve never checked the coolant concentration in your engine, you should, especially before winter rolling. If the coolant concentration is too low, it will freeze, which could cause significant and possibly irreparable damage to the engine. While the “floating ball” test tool works for ethylene glycol, a refractometer is more accurate and applies to all types of coolant.

Steve D’Antonio offers services to boat owners and buyers through Steve D’Antonio Marine Consulting.

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