24. SERVICE PROCEDURE 24.1.2 CLEAN INSIDE OF COOLING SYSTEM GENERAL The cooling system operates under pressure which is controlled by the pressure relief valve in the radiator cap. The gear-driven water pump circulates the coolant through the en- gine block, cylinder heads, radiator and engine oil cooler. Circulation is controlled by the thermostat which by-passes coolant flow around the ra- diator until the engine reaches operating temperature.
Proper cooling is possible only when the system is sealed, the radiator cap gasket is in good condition, the pressure relief valve and thermostats are operating properly, the system is free of coolant and air flow restrictions and the system is filled to the proper level. Selection and maintenance of the engine coolant is important to long engine life. The following information provides recommendations for selecting the engine coolant, maintaining the coolant inhibitors and servicing the cooling system. The system operates succesfully with a water/antifreeze mixture or inhibited/conditioned water as the coolant.
Water alone allows rust, scale deposits, and corrosion to occur within the system. After 4,000 hours or two years of operation, whichever comes first, the cooling system should be drained, flushed, and refilled as described in this section. For complete coolant specifications n SEE “20.4 COOLANT SPECIFICATIONS” on page 3-12 PC450-ENG 3-26 WARNING • Soon after the engine has been stopped, the coolant is hot and can cause personal injury. Allow the engine to cool before draining the coolant. • Since cleaning is performed while the engine is running, it is very dangerous to enter the rear side of the machine as the machine may suddenly start moving.
If the under cover is left removed, it may interfere with the fan. While the engine is running, never enter the rearside of the machine. • Never remove the radiator cap when the engine is at operating temperature. At operating temperature, the coolant is under pressure. Steam blowing up from the ra- diator could cause personal injury. Allow the engine to cool until the radiator filler cap is cool enough to touch with your hand. Remove the filler cap slowly to allow pres- sure to be relieved. WARNING