This engine has a pressure type cooling system. A pressure type cooling system has two advantages.
- The pressure helps prevent cavitation.
- The risk of boiling is reduced.
Cavitation occurs when mechanical forces cause the formation of air bubbles in the coolant. The bubbles can form on the cylinder liners. Collapsing bubbles can remove the oxide film from the cylinder liner. This allows corrosion and pitting to occur. If the pressure of the cooling system is low, the concentration of bubbles increases. The concentration of bubbles is reduced in a pressure type cooling system.
The boiling point is affected by three factors: pressure, altitude and concentration of glycol in the coolant. The boiling point of a liquid is increased by pressure. The boiling point of a liquid is decreased by a higher altitude. Illustration 1 shows the effects of pressure and altitude on the boiling point of water.
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| Illustration 1 | g00286266 |
The boiling point of the coolant also depends on the type of coolant and the concentration of glycol. A greater concentration of glycol has a higher boiling temperature. However, glycol transfers heat less effectively than water. Because of the boiling point and the efficiency of heat transfer, the concentration of glycol is important.
Three basic problems can be associated with the cooling system:
- Overheating
- Coolant loss
- Overcooling
If the cooling system is not properly maintained, solids such as scale and deposits reduce the ability of the cooling system to transfer heat. The engine operating temperature will increase.
When the engine is overloaded, the engine will run in the lug condition. When the engine is running in the lug condition, the engine is operating at a lower engine rpm that reduces the coolant flow. Decreased coolant flow during high load will cause overheating.
Coolant can be lost by leaks. Overheated coolant can be lost through the cooling system's pressure relief valve. Lower coolant levels contribute to additional overheating. Overheating can result in conditions such as cracking of the cylinder head and piston seizure.
A cracked cylinder head or cylinder liner will force exhaust gas into the cooling system. The additional pressure causes coolant loss, cavitation of the water pump, less circulation of coolant, and further overheating.
Overcooling is the result of coolant that bypasses the electric water temperature regulator and flows directly to the radiator. Low load operation in low ambient temperatures can cause overcooling. Overcooling is caused when the water temperature regulator remains open. Overcooling reduces the efficiency of operation. Overcooling enables more rapid contamination of the engine oil. This results in the formation of sludge in the crankcase and carbon deposits on the valves.
Cycles of rapid heating and cooling can result in cracked cylinder heads, gasket failure, accelerated wear, and excessive fuel consumption.
If a problem with the cooling system is suspected, perform a visual inspection before you perform any tests on the system.