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Coolant blues -- or greens

Agriculture.com Staff 07/07/2010 @ 9:10am

40% of diesel engine downtime can be attributed to coolant problems

Coolant gets no respect. The green stuff circulating through radiators is easily ignored since it often keeps working long beyond its prime to cool engines.

Yet coolants do more than cool; they must protect engine parts in the process. Failing to do so causes approximately 40% of diesel engine downtime, engineers estimate. "A fresh fill of antifreeze is good insurance against trouble and costly repairs," says Utah State University Extension engineer Von Jarrett.

Major problems relating to cooling breakdowns include metal corrosion, cavitation, scale deposits, and inhibitor dropout or green goo.

Corrosion is the natural tendency of metals to revert to their ore form. "All metals exposed to coolant will corrode," says Frank Cook of Old World Industries, a coolant manufacturer. "Proper coolant chemistry slows the rate of corrosion by forming a protective layer on metal surfaces," he says.

Borate, for example, is an inhibitor that maintains pH between 8.5 and 11, providing protection for iron and steel components. Silicate and nitrite in coolant protect aluminum and ferrous metals like iron and steel.

Nitrite actually does double duty, protecting wet-sleeve cylinder liners against cavitation. This form of metal erosion occurs during an engine's power stroke, which causes the outside wall of a liner to move away from the coolant and create, for an instant, a near vacuum. This low-pressure pulse causes the surrounding coolant to boil and to form tiny bubbles.

The liner then returns to its position at high velocity and presses against the bubbles. The bubbles implode (collapse) against the liner wall surface at pressures up to 60,000 psi and blast small pits in the steel. Nitrite forms a thin protective film on the liner wall and acts as a barrier against pitting.

Unlike cavitation, scale adds to liners and other surfaces in an engine's cooling system. Only 1/16 inch of scale reduces heat transfer efficiency by 40%. Since scale tends to form in specific areas of the hot side of the engine, it causes localized hot spots and distortion. The harder the water being used in a coolant, the greater the amount of scale formation. This is why deionized water is used in coolants.

Too high a concentration of two common antifreeze inhibitors Ð phosphate and silicate Ð can also cause overheating by coating coolant system surfaces with green goo. This situation, called inhibitor dropout, occurs in a lot of failed water pumps, thermostats, radiators, and heater cores.

The key to avoiding green goo is to use a "high-quality, fully formulated precharged coolant," says Craig Gullett of Fleet Charge, an automotive supplier. He urges using a fully formulated diesel coolant that meets The Truck Maintenance Council Recommended Practice RP-329. Look for this designation on the coolant label.

Download a PDF file of the Machinery Digest section from the Mid-February issue of Successful Farming.

40% of diesel engine downtime can be attributed to coolant problems

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