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  • The operation and maintenance of the cooling system is critical to engine durability and reliability.
  • The flame temperature of diesel fuel is approximately 3900° F (2149° C); sustained operation of the engine at this temperature without some means of removing heat quickly results in damaged or destroyed engine components.
  • Diesel engine heat loads include EGR, lubrication oil, and the air intake system.
  • An important job of the cooling system is to raise engine coolant temperature quickly to keep engine component wear to a minimum.
  • Machined parts operating with close tolerances require consistent operating temperatures of 180—200° F (82—93° C); some exceptions are emergency and military engines that are designed to withstand as much as 230° F (110° C).
  • As engine coolant warms, it expands; cooling systems must provide for this expansion.
  • Cooling systems are pressurized to maintain greater than atmospheric pressure at the water pump inlet and to increase the boiling point of water.
  • Cooling systems must provide for the deaeration of coolant to prevent pumps and coolant passageways in the cylinder head from becoming air-bound.
  • Antifreeze contains a number of additives that minimize electrochemical reactions, which prolongs the durability of engine and cooling system components.
  • Maintenance practices and engine coolant formulations should be designed to minimize the formation of engine-damaging deposits.
  • Freeze and boil protection are both provided by the use of antifreeze; additional boiling protection is accomplished through pressurizing the cooling system.
  • Cylinder wall and liner cavitation is a condition unique to diesel engines; chemical treatment of the cooling system is a preferred method for minimizing cavitation erosion.
  • Coolant generally flows through the oil cooler first, through the cylinder block water jackets next, and then through the cylinder head last.
  • HD and automotive diesel engines depend almost exclusively on the efficiency of liquid cooling systems.
  • Diesel coolant consists of water, antifreeze (which contains a corrosion-inhibitor package), and supplemental coolant additives that minimize cavitation erosion.
  • One major factor in the corrosion rate of an engine’s metals is the coolant’s pH.
  • Water is the most efficient fluid to transfer heat; however, water will corrode metal parts in contact with the cooling system; therefore, corrosion inhibitors must be added.
  • Antifreeze is added to water, which increases the boiling point and lowers the freezing temperature of water.
  • Most antifreezes are made with a base of either ethylene glycol or propylene glycol.
  • Mixing ethylene glycol or propylene glycol antifreeze with water alone is an effective method for preventing the corrosion or erosion of cooling system components; additive packages are used to enhance antifreeze.
  • Radiators are heat-exchanging devices that release heat absorbed from the engine into the air.
  • While early radiator caps simply prevented coolant from spilling out of the cooling system, today’s radiator caps have additional functions, such as increasing the pressure of the cooling system to raise the boiling point of coolant and allowing air or coolant to re-enter the cooling system when the pressure drops after the engine cools.
  • Surge or overflow tanks provide the space for coolant and vapor to move when the engine coolant is hot.
  • Vent lines located at the highest points on the engine and radiator bleed steam and air out of the engine and into the surge tank.
  • To ensure positive circulation of coolant, an engine-driven water pump is used to move coolant through the cooling system.
  • Water filters on diesel engines, if equipped, perform two primary purposes. First, they remove sediment, rust, and dissolved particles that can cause abrasive damage to the cooling system. Second, they supply additives to the coolant.
  • Thermostats regulate the temperature of the engine coolant by modulating or controlling the volume of coolant circulated to the radiator.
  • Engine fans are designed to increase the airflow across the radiator, which improves the efficiency of heat removal from coolant.
  • Fan shrouds seal the gap around the fan and radiator to ensure that cooling air runs through the radiator rather than leaking around its sides or past the headlights.
  • The upper and lower radiator hoses and heater hoses require flexible connections between the engine radiator and the heater core due to engine vibration and torque flexion.
  • The cooling system must be maintained on a regular basis to prevent overheating, cavitation, corrosion, scale, and gelation due to silicate dropout.
  • OBD systems are required to monitor the cooling system for proper operation.

 

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