Lesson 5/Learning Event 2
If the coolant pump does not pump, the coolant will not flow through the system well enough to keep the
engine cool. The coolant pump will fail to operate if the impeller comes loose from the pump shaft or the
shaft breaks. This may happen if the engine is started and the coolant is frozen. In any event, if the pump
does not operate it must be replaced.
Loss of Coolant
If the complaint is that the cooling system is losing coolant, the trouble is most likely caused by a leak. The
most likely spots where leaks occur are at the hoses, drain cock, cylinder head gasket, radiator cap, coolant
pump, radiator, and cracks in the cylinder head or block. When a leak cannot be stopped by tightening, the
leaky part must be replaced.
Engine Fails to Reach Operating Temperature
The temperature gage may not reach the normal operating range in a reasonable time when the engine is
started. This could be caused by a faulty thermostat or gage circuit. The thermostat may be faulty or be of the
wrong heat range. You would have to remove, inspect, and test the thermostat to check this. If the
temperature gage does not indicate any temperature, but the engine gets warm, the trouble will be a defensive
gage, wiring, or gage sending unit.
In this lesson, the major topics for discussion have been why an engine cooling system is needed; why the
engine needs some heat; the three jobs of the cooling system; how fuel, oil, and exhaust aid the cooling
system; how the liquid-cooling system parts are constructed and operate; how to inspect and repair cooling
system parts; how to do preventive cleaning of the cooling system; and how to troubleshoot the cooling system.
If there is any part of the lesson that you do not understand, go back and review that part of the lesson. Then
turn to the practice tasks at the end of this lesson and do all of the suggested tasks that you can.