When does the water pump need to be replaced?

A working water pump is vital for the engine; if it doesn't work, the engine will overheat. An engine can survive mild overheating, but severe overheating can damage it.
Water pump Water pump. See more illustrations: Fig 1, Fig 2, Fig 3.
For this reason, if your engine temperature rises above normal, have the cooling system checked as soon as possible.

When does the water pump need to be replaced? The water pump doesn't need to be changed in regular mileage intervals. It must be inspected during regular services and replaced if it shows early signs of failing. The water pump also needs to be replaced if it breaks down. In some cases a water pump is replaced as a precaution; for example, when changing the timing belt, or when dealing with overheating issues or in cars that are known for water pump failures.

How a water pump works: The water pump creates the flow within the cooling system of a car engine. It's called a water pump because in the early days of automobiles an engine cooling system was filled with water. Modern cars use a special fluid called antifreeze or coolant.
Water pump in a car engine cooling system Water pump creates the flow in the engine cooling system. See another illustration: Fig1.
How the engine cooling system works, see the diagram: The thermostat blocks the circulation through the radiator when the engine is cold; it opens and allows the circulation when the engine reaches normal operating temperature. As the hot coolant passes down through the radiator, it cools down. The water pump draws the cooled coolant back out of the radiator. See the photo of the water pump and thermostat.

In the majority of today's cars, a water pump is a mechanical device rotated by a drive belt. The drive belt itself is driven by the crankshaft pulley of the engine. In some cars, a water pump is driven by a timing belt or timing chain. Other cars have an electric water pump that is operated by an electric motor.

What are the signs of a failing water pump? One of the signs is coolant leaking from the water pump. The water pump has a weep hole in the lower portion; see the photo. A small amount of dry coolant residue around the weep hole is normal, but coolant leaking from the weep hole is a sign that the pump is on its way.
Water pump Water pump.
Car makers provide guidelines for mechanics on when a water pump is considered bad and needs replacing. Sometimes coolant leaks from the pump seal or O-ring. A coolant leak from the pump usually shows as a pinkish or greenish residue, depending on the color of the coolant. Often, leaking coolant is splashed by a drive belt, and it looks like a whitish residue around the drive belt and surrounding area.

A failing water pump can also cause intermittent grinding or rumbling noise in some vehicles. In this case, a mechanic will have to diagnose the source of the noise, before condemning the water pump. For example, a mechanic may find that the water pump shaft feels loose, which means the pump is bad.

In many modern cars, the impeller inside the water pump is made out of plastic and can crack and come loose on the shaft. A metal impeller is stronger, but can also be damaged by corrosion at higher mileage. In either case, the flow of coolant will be reduced or stopped completely and the engine will overheat. The heating system inside the car will also stop working, as it relies on coolant flow. Mechanics can check for coolant flow by comparing the temperature of different parts (hoses) of the cooling system. In some cars, a flow of coolant is visible in the expansion tank.

Replacing a water pump with a timing belt/chain: If the water pump is driven by the timing belt, it is also often replaced as a precaution during the timing belt replacement.
Water pump In this Volkswagen engine, a water pump is driven by a timing belt.
The reason is that it takes only a little extra labor to replace a water pump when doing the timing belt because it's in the same location.

Is it necessary to replace a water pump with a timing belt? No, but it's an option worth considering. For example, if you check an owners manual for one of the Honda vehicles with a V6 engine, it says "Replace timing belt and inspect water pump." Many Honda owners, however, opt to replace the water pump together with the timing belt because if the water pump fails later it will cost the same labor to replace. Plus, a water pump is not a very expensive part ($45-$170).

For the same reason, if a water pump is driven by a timing chain, a mechanic may recommend replacing it as a precaution if some work is done with the timing chain or in the same area. Again, it's not necessary, but it will be a lot more expensive replacing it later, since many parts will have to come off to get to the water pump.

If the engine has been overheated because of a broken down water pump, there is always a chance that it might have suffered some other damage as a result. It all depends on the severity of overheating. However, a mechanic may not be able to check for further engine damage until the water pump is replaced and the engine is started. In cases like this, your mechanic may recommend considering all of your options before doing repairs.

How much does it cost to replace a water pump? It depends on the water pump location. In most cars, a water pump is located outside of the engine and is not very difficult to replace.
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For example, replacing a water pump in the 2009-2013 Toyota Corolla is fairly easy and costs around $300-$450 parts and labor. On the other hand, changing the water pump in the 2007-2014 Ford Edge V6 engine might cost over $2,000, since the water pump is driven by a timing chain and is located inside of the engine.

Often, parts like a thermostat or a drive belt are replaced together with a water pump. These parts are not very expensive.

After the water pump is replaced, the cooling system must be bled properly to remove air pockets from the system. One of the signs of air in the cooling system is when there is no heat from the vents at idle with the heater is on and the engine is running. Normally, the heater should provide a good heat at any engine speed.