How to Tell if a Car's Water Pump Needs Replacementby Robert Tomashek
Internal and external water pumps are like night and day when determining a possible failure. While external pumps can be seen visually and are typically easier to replace, internal pumps are buried in the engine and can take hours to access.
External water pumps have what is known as a weep hole in them. This hole allows coolant to leak from the water pump as an early sign of bearing failure. When this occurs, it will tend to leak more when the engine is running than when it is turned off. If the water pump is leaking you must replace it.
Noise and Binding
When the bearing supporting the water pump shaft fails it can begin to make noise. You may hear a grinding or knocking noise from a failing water pump bearing. Remove the belt that drives the pump and spin the pulley by hand, feeling for roughness or looseness in the shaft. Replace the pump if any of these signs are evident.
The lack of coolant flow from a worn water pump can cause low speed overheating. This symptoms does not initially show up at higher speeds. This can be the only indicator that an internal pump is beginning to fail.
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