The function of the coolant system is to maintain a specified operating temperature for the engine. Some of the
heat generated by the engine is absorbed by the coolant flowing through the passages in the cylinder block and
head. Then, heat is removed from the coolant as it flows through the radiator. When you troubleshoot overheat
ing, remember that too much oil in the oil pan can cause additional heat from friction when the rod journals are
submerged in oil.
Overfilling with oil raises the oil temperature which is transferred to the coolant system at the oil cooler.
The system is designed to use a specific quantity of coolant. If the coolant level is low, the engine will run hot.
NOTE: The engine or system has a leak if frequent addition of coolant is necessary. Find and repair the leak.
During operation entrapped air mixes with the coolant which results in cavitation corrosion and poor heat trans
fer. Highly aerated coolant can cause’localized overheating of the cylinder head and block which can result in a
cracked head, scored cylinder or blown head gasket.
During filling, air must be vented from the engine coolant passages. The air vents through the “jiggle pin” openings to the top radiator hose and out the fill opening.
Additional venting is provided for engines equipped with an aftercooler. Open the petcock during filling.
NOTE: Adequate venting is provided for a fill rate of 14 liters/minute [3.5 U.S. Gallon/minute].
NOTE: A 50 percent mixture of antifreeze and water must be premixed before filling the system. The ability of antifreeze to remove heat from the engine is not as good as water, so pouring antifreeze into the engine first could contribute to an over heated condition before the liquids are completely mixed.
A mixture of 50% ethylene-glycol base antifreeze is required for operation of the engine in temperature environments above -37°C [-34°F]. A mixture of 40% water and 60% antifreeze is recommended for temperatures below -3 7 °C [-34°F]. Never use more than 60% antifreeze.
Caution: Never use water alone for coolant. Damage from corrosion can be the result of using water alone for
coolant. The small holes in the head gasket are especially susceptible to plugging. These holes are orifices
and their size is critical. Do not enlarge the size of the orifices. To do so will disturb the coolant flow and will
not solve an overheating problem.
Water will cause rust formation reducing the flow in the smaller coolant passages.
Also, water used as a coolant for even a relatively short period can result in the cup plugs rusting through allowing the coolant to leak.
NOTE: A sudden loss of coolant from a heavily loaded engine can result in severe damage to the pistons and
cylinder bore.
