1. Purposes and Functions of the Cooling System

1.5. Temperature Regulation

LO 11-02: Identify and explain the purposes and functions of the cooling system.

 

Temperature Regulation

Another important job of the cooling system is to raise engine coolant temperature quickly to keep engine component wear to a minimum by circulating it through the engine Figure 10. Machined parts operating with close tolerances are designed for consistent operating temperatures of between 180–200° F (82–93° C), with one exception being emergency and military engines that are designed to withstand as much as 230° F (110° C).

Higher cooling system operating temperatures lower the amount of heat rejected, but if temperatures climb even as little as 12° F (−11° C) beyond normal range, cylinder wall wear begins to dramatically increase. Conversely, cold cylinders prevent engine parts from operating at optimal clearances and lead to excessive oil consumption, carbon deposits on pistons, poor combustion quality, and oil sludging due to water condensation. It is important to remember that in current diesels, the coolant must reach a minimum temperature necessary within a reasonable time to enable other on-board diagnostic (OBD) monitors to run. This explains why fault codes for the cooling system are set if the engine does not quickly reach operating temperature.

  Technicians Tip  
  Short-run operation of any engine causes sludging of the engine oil. If oil is not allowed to properly heat up, water condensation from blowby gases contaminate the oil, which can eventually clog the oil pickup tube for the oil pump and other oil passages in the engine. Crankcase ventilation system filters can also clog with sludge and heavy blowby particulate. They may even freeze due to extended cold-weather, low-temperature engine operation. Technicians may need to verify that engine oil is frequently brought to operating temperature and maintained in the correct operating range by the cooling system to vaporize any water condensation in the lubrication oil.  
  Fig11_10

FIGURE 11-10: Typical coolant circulation pattern in a V8 diesel.

 

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