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Water Pump Diagnosis & Replacement
Copyright AA1Car
The water pump is the heart of the cooling system. The pump circulates coolant between the engine and radiator to keep the engine from overheating. Inside the pump is a metal or plastic impeller with blades that push the water through the pump. The impeller is mounted on a shaft that is supported by the pump housing with a bearing and seal assembly. The water pump is usually belt driven and is mounted on the front of the engine.
WATER PUMP PROBLEMS
Water pumps typically fail one of two ways: the shaft seal starts to leak, or
the impeller inside breaks, comes loose or the blades erode and wear down (which is more of a problem with pumps that have plastic impellers).
When a water pump starts to leak, the cooling system will lose coolant. If the leak is not discovered, the loss of coolant will eventually cause the engine to overheat. The drive may not realize anything is wrong until the temperature warning light comes on. If this happens to you, shut the engine off immediately. Severe engine damage can result if an overheating engine is driven too far.
If the engine has overheated, the entire cooling system (radiator, hoses, water pump and engine) must all be inspected to see if there are any coolant leaks. If coolant is leaking out of the water pump shaft or vent hole, the water pump needs to be replaced. Cooling system sealer cannot stop this kind of leak.
WATER PUMP SEAL FAILURE
A seal on the water pump shaft prevents coolant from leaking past the bearing. Seal wear can be caused by rust, sediment or other contaminants that are circulating with the coolant inside the cooling system. The pump shaft and bearings are also under constant load not only from the drive belt or timing belt but also the fan on vehicles with pump-mounted mechanical cooling fans. Eventually the water pump shaft seal and/or bearing wears out and the pump begins to leak.
Most OEM water pumps are designed to go 100,000 miles or more, but they don't always go the distance. It's not unusual to see leaks occur after 50,000 or 60,000 miles. If the pump shaft shows any visible wobble or the bearings are making noise, the pump should be replaced even if it isn't leaking (because it soon will be!).
WATER PUMP FAILURES
Sometimes a water pump will fail internally due to severe corrosion wearing away the impeller blades, or the impeller comes loose on the shaft, or the shaft itself may break from metal fatigue (caused by flexing due to an out-of-balance fan).
Many late model vehicles (Chrysler in particular) have plastic impellers to improve cooling efficiency and to reduce cavitation (drag). But the plastic can wear down quickly if the coolant is dirty and contains abrasives. The pump may not leak, but it may not circulate enough coolant through the engine to keep the engine at normal operating temperature.
One way to test for a bad water pump is to squeeze the upper radiator hose when the engine is hot and idling. Careful, because teh hose willb e HOT! If you do not feel much coolant circulating through the hose when you rev the engine, the pump may be bad. The other cause might be a bad thermostat that is not opening properly (remove and inspect the thermostat), or a clogged radiator.