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Diesel Truck Cooling

Heat, sometimes expressed as Btus or British thermal units, is the one item that every diesel engine has in abundance. One Btu is the amount of thermal energy necessary to raise the temperature of one pound of water by one degree Fahrenheit. As diesel fuel burns, it produces heat; this heat creates the energy the engine produces. Working under "normal" operating conditions, a diesel engine's combustion cycle will produce thousands of Btus. These engines must operate under extreme temperatures for several reasons. Diesel fuel is much less volatile than gasoline and therefore requires greater compression and higher temperatures to burn efficiently. Also, in order to comply with tougher emissions laws, diesels must run hotter to burn cleaner. Stringent emissions rules aside, the demands on today's diesel engines are greater than ever before. Increased payloads, turbochargers and auxiliary heating and air conditioning systems are just a few of the items placing energy demands on a diesel engine and, in turn, it's cooling system.

The hardest working system on today's computer controlled, high horsepower, high efficiency, high fuel mileage diesels is the cooling system. Diesel engine technology has made these engines perform cleaner than ever. At the same time, the heat or Btus generated by the newer diesels has increased as much as 10% over previous models. Keeping these monsters cool is a big job that's getting bigger. In the next two years alone, diesel engine manufacturers are claiming that engine operating temperatures will increase by more than 30% due to even tougher emissions standards that's a 30% increase in an engine that already produces enough excess heat to completely destroy itself! How are truck manufacturers planning to deal with all of the excess heat?

Bigger radiators are not an option. In the search for increased fuel mileage, today's trucks have become very aerodynamic. The new nose designs leave little room for increased cooling system capacity. Truck engineers have turned to better-designed fans, pumps and coolant passages in order to shed excess heat. But the radiator is usually the center of attention when trying to find ways to increase cooling system efficiency. Depending upon the rated horsepower, a Class 7 or 8 truck's radiator core can be anywhere from 900 to over 1,400 square inches. Since engineers cannot increase the size of the radiator, they have found ways to better manage the airflow to and through the radiator. In addition, they have improved tube and fin design for maximum heat-shed ability. Underhood temperatures and air charge delivery temperatures have also been controlled in an effort to reduce total excess heat. Industry experts have determined that even a minor reduction in cooling system function can cause a modern diesel engine to self-destruct.

So what does all of this information mean to the shop owner? To better understand we must first look at what exactly makes up the cooling system on a modern diesel. The cooling system includes the water jackets that surround each cylinder; water passages within the engine block and head(s); water pump; radiator; engine fan and external electric fan(s); thermostat; hoses; heat and temperature sensors and the charge air cooler. While the charge air cooler is not part of the cooling system, one must take into account that the charge air cooler lowers the temperature of the intake air. By doing so, there is an increase in the engine's combustion temperature and, in turn, an increase in the efficiency of the combustion cycle. By utilizing more of the generated heat for energy, there is a reduction in the amount of excess heat generated.

A properly operating charge air cooler can reduce excess heat by as much as 40% in a modern diesel. Intake air temperatures are now within the 110-degree F range in comparison with older diesels that operated with intake temps above 180 degrees F. In addition, electric fans that trigger when temperatures rise, force additional air through the cooler and radiator cores to help control temperatures. This is especially important when road speed drops (when stuck in traffic or pulling a steep grade). The remainder of the cooling system is designed to operate with the decreased temperature(s).

A modern diesel truck must have its cooling system maintained impeccably, to avoid unexpected costly repairs, and radiator failure. Operators must understand the importance of preventive maintenance. A regular inspection of the entire cooling system is necessary. Maintaining proper air flow through the charge air cooler and radiator is of the utmost importance in preventing costly breakdowns and costly repairs.

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