The engine cooling system uses a coolant solution of DEX-COOL™ and clean, drinkable water. The system carries excess heat away from the engine block and the air compressor, if equipped. A belt driven water pump moves the solution through the engine cooling system. The heated coolant flows through the radiator, where heat is transferred to the outside air. The cooled fluid then flows back to the engine block.
The coolant dissipates heat as the coolant passes through the radiator tubes and the radiator. Radiators transfer heat from the coolant to the outside air. The engine cooling fan pulls outside air past the radiator fins and the tubes.
The fan draws the air through the radiator fins in order to cool the radiator and the coolant. A fan shroud and rubber baffles direct air flow. The rubber baffles are mounted to the under side of the cab. The fan shroud and the rubber baffles form a seal at the top of the radiator. Together the fan shroud and the baffles prevent air from re-circulating around the radiator. Missing or misaligned baffles may cause overheating.
A thermostatic fan clutch from the engine crankshaft belt drives the fan. The thermostatic fan clutch controls the torque that transmits from the engine crankshaft to the fan blades. The clutch allows more torque to engage on the fan when the following conditions exist:
| • | Increasing engine temperature |
| • | Low driving speeds |
The fan turns faster and draws more air through the radiator with more torque. The thermostatic fan clutch disengages when the following conditions exist:
| • | Decreasing engine temperature |
| • | Higher driving speeds |
Thermostats regulate the engine operating temperature. The thermostats are located in the coolant outlet at the front of the engine. When the engine reaches a predetermined temperature, the thermostats open and allow the coolant to flow through to the radiator. The thermostats close as the engine cools down in order to restrict coolant flow. The thermostats also control the amount of coolant that flows through the engine.
The cooling system operates under pressure in order to increase the efficiency of the cooling system. Operating the system under pressure causes the following actions:
| • | Reduces boiling at high engine coolant temperatures |
| • | Reduces boiling at high altitudes |
| • | Prevents cavitation |
| • | Raises the boiling point of the coolant |
The pressure cap on the radiator or on the surge tank regulates the cooling system pressure. The pressure cap is designed with two normally closed valves. The pressure relief valve opens when the coolant temperature and the pressure exceed the pressure valve spring tension. The pressure relief valve allows coolant or air to escape. The pressure relief valve is set for 62 kPa (9 psi). The vacuum valve opens when the coolant is cooling and when ambient pressure overcomes the vacuum valve spring. The vacuum valve allows the coolant in the recovery reservoir or the surge tank to re-enter the system. The vacuum valve also prevents the collapse of the hoses or other components that are not internally supported.
The coolant recovery reservoir or the surge tank is mounted behind the cab. Coolant recovery reservoirs or surge tanks compensate for coolant fluid expansion. Coolant recovery reservoirs or surge tanks also help remove air from the cooling system.
