Staying Cool

It is virtually impossible to overstate the importance of an engine's cooling system because it directly affects how reliable and durable the machine will be in the field. OEM engineers must work closely with their engine manufacturer and/or distributor on the design and selection of an engine's cooling system.

It's important for equipment engineers to understand the key components of the cooling system because of their effect on the equipment's overall performance.

The main job of the cooling system is to reduce engine temperature. The cooling system removes heat from the engine by transferring it from the engine to the coolant. Once coolant is moved to the radiator, the air temperature increases, decreasing the coolant temperature by 5 to 10 F. This process repeats itself, circulating coolant throughout the engine.

The core components of the cooling system include the radiator, the fan and its shrouding, coolant lines, coolant pump, thermostat, coolant jackets, and the charge air cooler. Some engines also utilize an exhaust gas recirculation (EGR) cooler. Most engine manufacturers don't supply components that are external to the engine, such as the radiator, directly from the factory. OEMs will typically need to work with their engine distributor or another resource to complete the cooling system.

Experts at John Deere Power Systems offer the following advice to help OEMs ensure that an application's engine and cooling system work together to keep the equipment running smoothly.

Aftercooling

An engine's aspiration can involve the cooling system and directly affects the equipment's performance.

Diesel engines can have four kinds of aspiration: natural aspiration, turbocharging, liquid-to-air aftercooling and air-to-air aftercooling. Liquid-to-air aftercooling and air-to-air aftercooling affect the engine's cooling system. Air-to-air aftercoolers and engine radiators require a fine balance between the systems to maintain optimum charge-air temperatures and coolant temperatures across the engine's operating range.

Air-to-air and liquid-to-air aftercooled engines have a higher power density than engines that are only turbocharged or naturally aspirated. The more power density an engine has, the more horsepower it generates in a smaller displacement. When the air going into the engine cylinders is cooled, engineers can calibrate higher power ratings, thus increasing power density. Liquid-to-air aftercooled engines use coolant, which runs at about 180 F, to lower the temperature of the air coming out of the turbo (about 200 to 300 F) before it's routed back to the cylinders. The most power-dense form of aspiration is air-to-air aftercooling, which uses ambient air to lower the temperature of the air from the turbo.

The aftercooler and the cooling fan are not only crucial to performance but are also key to emissions compliance. The performance of the aftercooler affects the temperature of the combustion in the cylinder and lowers the amount of NOx produced.

Coolant

Engines must be shipped without coolant, so OEM customers are responsible for filling and maintaining the engine's cooling systems. Almost all diesel engines use glycol-based heavy-duty coolant, although a few engine manufacturers make oil-cooled engines. Knowing the best coolant solution for an engine is vital to preventing cylinder liner erosion, pitting and corrosion damage to aluminum engine components.

Heavy-duty diesel engine coolant should be comprised of deionized or distilled water and ethylene glycol or propylene glycol. Ethylene glycol concentrate must be low-silicate and meet ASTM D4985. High-silicate ethylene glycol is for use in automotive applications and should not be used in diesel engines.

Propylene glycol must also be low-silicate. The chemical properties of propylene glycol and ethylene glycol are different, and they should not be mixed. The system must be flushed before changing mixtures.