Water Pump Diagnosis & Replacement
The water pump is the heart of the cooling system. The pumpcirculates coolant between the engine and radiator to keep the engine fromoverheating. Inside the pump is a metal or plastic impeller with blades thatpush the water through the pump. The impeller is mounted on a shaft that issupported by the pump housing with a bearing and seal assembly. The water pumpis usually belt driven and is mounted on the front of the engine.
WATERPUMP PROBLEMS
Water pumps typically fail one of two ways: the shaft seal startsto leak, or the impeller inside breaks, comes loose or the blades erode andwear down (which is more of a problem with pumps that have plastic impellers).
When a water pump starts to leak, the cooling system will losecoolant. If the leak is not discovered, the loss of coolant will eventuallycause the engine to overheat. The drive may not realize anything is wrong untilthe temperature warning light comes on. If this happens to you, shut the engineoff immediately. Severe engine damage can result if an overheating engine isdriven 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 anycoolant 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 thiskind of leak.
WATERPUMP SEAL FAILURE
A seal on the water pump shaft prevents coolant from leaking pastthe bearing. Seal wear can be caused by rust, sediment or other contaminantsthat are circulating with the coolant inside the cooling system. The pump shaftand bearings are also under constant load not only from the drive belt ortiming belt but also the fan on vehicles with pump-mounted mechanical coolingfans. Eventually the water pump shaft seal and/or bearing wears out and thepump begins to leak.
Most OEM water pumps are designed to go 100,000 miles or more, butthey don't always go the distance. It's not unusual to see leaks occur after50,000 or 60,000 miles. If the pump shaft shows any visible wobble or thebearings are making noise, the pump should be replaced even if it isn't leaking(because it soon will be!).
WATERPUMP FAILURES
Sometimes a water pump will fail internally due to severecorrosion wearing away the impeller blades, or the impeller comes loose on theshaft, or the shaft itself may break from metal fatigue (caused by flexing dueto an out-of-balance fan).
Many late model vehicles (Chrysler in particular) have plasticimpellers to improve cooling efficiency and to reduce cavitation (drag). Butthe plastic can wear down quickly if the coolant is dirty and containsabrasives. The pump may not leak, but it may not circulate enough coolantthrough the engine to keep the engine at normal operating temperature.
One way to test for a bad water pump is to squeeze the upperradiator hose when the engine is hot and idling. Careful, because the hose willbe HOT! If you do not feel much coolant circulating through the hose when yourev the engine, the pump may be bad. The other cause might be a bad thermostatthat is not opening properly (remove and inspect the thermostat), or a cloggedradiator.
HOW TOREPLACE A WATER PUMP
Replacement water pumps come in a wide variety of shapes and sizesas well as shaft lengths, and on some engines more than one style of pump maybe used. Finding the right pump means matching not only the year, make, modeland engine, but sometimes also the VIN or casting number. If possible, comparethe replacement pump to the old pump to make sure it is the right one for theapplication. To consolidate applications, some replacement castings have extraoutlets and mounting bosses or bolt holes so it can be used on a wider varietyof engine applications. This is okay as long as there are enough outlets andmounting bosses to match the original casting.
To Replace Your Old Water Pump:
1. Drain the radiator. Open the petcock valve at the bottom of theradiator, or if there is no drain valve, loosen the lower radiator hose. Dothis when the engine is COLD. Catch the coolant in a bucket for reuse later, orsafe disposal if it is time to change the coolant. Use antifreeze can usuallybe flushed down the toilet. DO NOT dump it into a storm sewer or on the groundbecause it is toxic and will kill plants. It is also poisonous to animals andpeople.
2. Remove the fan belt. On engines with a serpentine belt drive,this means loosening the tension on the automatic tensioner. Note how the beltis routed BEFORE you remove it so you can reinstall it later correctly (draw apicture if there is not a belt decal under the hood that shows how the belt isrouted around the pulleys).
3. Remove anything else that is the way. This may include the fan,fan shroud, timing belt cover if the pump is driven off the timing belt on anOHC engine instead of a serpentine belt, or any brackets or otherengine-mounted accessories that are blocking access to the pump.
4. Unbolt the water pump from the engine.
5. Clean the pump mounting surface to remove all traces of oldgaskets. The mounting surface must be clean and dry befoe you install the newpump.
6. Position the gasket on the new pump, using gasket sealer oradhesive as required, then bolt the new water pump to the engine. Use threadsealer on any threads that screw all the way through into open water jackets(not needed with blind bolt holes).
7.Refill the cooling system. Be patient because it may take sometime for all the air to vent out. Many cooling systems have vent valves thatcan be opened during a refill to allow air a place to escape.
Cooling System Notes:
If the cooling system contains rust or sediment, the radiator andblock should be cleaned and flushed BEFORE you remove the old pump to protectthe new pump from possible damage.
If the coolant that you drained out of the radiator is rusty ordirty, do not reuse it. Refill the cooling system with a 50/50 mixture of newantifreeze and clean, distilled water. Do not use tap water or softened waterbecause it contains minerals and salts that can cause corrosion inside thecooling system.
If your vehicle has a pump-mounted mechanical fan with a fanclutch, the fan clutch should also be replaced at the same time. The servicelife of the fan clutch is about the same as the pump. A slipping fan clutchwill reduce radiator cooling and may cause the engine to overheat.
Other parts you may need to complete the job include a newthermostat (recommended if you are having an engine overheating problem),new radiator and heater hoses (hoses that are cracked, brittle or unusuallysoft should be replaced), and new hose clamps.