Lesson 5/Learning Event 2
A coolant pump may be defective due to faulty bearings, leaks, or failure to pump. The coolant pump is
checked with the engine stopped and then again when it is running.
With the engine stopped, check the pump bearings for looseness by attempting to move one of the fan blades
back and forth lengthwise with the pump shaft. Do not exert enough force to bend the fan. Since the fan is
bolted to a hub on the coolant pump, any slack felt in the fan is caused by loose bearings on the pump shaft.
Unless the coolant pump leaks bad enough to drip, the leak can be hard to locate. The coolant usually leaks
past the pump shaft seal and then escapes through a drain hole in the pump housing. The drain hole is located
on the bottom of the housing, and on most vehicles it is covered by the belt pulley. However, it can usually be
viewed by using a small mirror or flashlight. Any dampness or water stains left by evaporation around the
drain hole indicate a coolant leak.
On some vehicles you can look in the radiator filler neck to see if the pump is operating. Run the engine until
the thermostat opens; then look through the filler neck into the radiator. If you see the coolant circulating, the
pump is operating. If the radiator inlet or baffles in the radiator tank prevent you from being able to see the
circulation of coolant, squeeze the upper radiator hose almost together. Accelerate the engine. If the pump is
operating, you can feel the coolant force its way through the hose.
The coolant pump should be replaced if it has loose bearings, is leaking, is noisy, or does not operate.
If the thermostat fails to close, the engine will warm up slowly. If it fails to open, the engine will overheat.
When thermostat trouble is suspected, the thermostat should be removed and tested. The thermostat is located
at the coolant outlet of the engine.