Automotive water pump

Bad Water Pump: Signs, Symptoms And How To Fix It

The water pump in your car functions like the heart of your cooling system. It pumps water through the entire engine and back to the radiator. Without the constant flow of water cooling it down, your engine would quickly overheat. Not only will an overheating engine leave you stranded on the side of the road but overheating might also cause the engine to seize. Learning to detect the signs of a bad water pump early can save you thousands in repair bills. Luckily,  replacing a water pump is not a difficult task on most car models. In the case you have to deal with a bad water pump on your vehicle, we’ve created this post to help you identify the most common bad water pump symptoms and what you can do to fix it. So take out your tools and get ready to save some money on your next water pump replacement

Automotive cooling system

How a Water Pump Works

A car’s water pump is driven by a belt on the front of the engine. Most modern cars today use a serpentine belt to drive the water pump along with other accessories like the air conditioning system and alternator. However, other cars use the timing belt or chain to drive the water pump. While a serpentine driven water pump is usually easier and quicker to replace, a timing belt driven one has the advantage to keep working even if the serpentine was to break.

As the water pump rotates, an impeller blade pulls water from the engine and pushes water back out. Once the coolant reaches normal operating temperature, the thermostat opens and lets the coolant flow into the radiator. The radiator allows water to dissipate heat and, once cooled down, returns it to the engine. Cooling system passages through the engine allow the water to absorb heat and carry it back to the water pump. And the cycle starts all over again.

Overheating car engine

Signs of a Bad Water Pump

If you know what to look for, you can usually catch the signs of a bad water pump before serious damage has happened to your engine. In other circumstances, and depending on the cause of the failure, the symptoms might be a bit difficult to notice. Here are some of the most common signs letting you know that your water pump is letting you down and needs to be replaced.


The easiest sign to notice is the engine’s temperature being higher than usual. The temperature on most cars should usually rise gradually and then stay still. Most vehicles have two dots or lines around the middle of the temperature gauge and the needle should stay between the two at all times while driving.

If the water pump becomes faulty and the impeller stops turning, the water will stop circulating through the engine. Once the water flow stops, the temperature will quickly rise and should hit the red line quite quickly. If the impeller is loose and doesn’t spin at a constant speed, the temperature might also fluctuate and you might notice the needle going up and down intermittently.

Be warned, though. Many other faulty cooling system components might also cause the same symptoms. A stuck thermostat or bad radiator may also cause your car to overheat. It could even be caused by a cracked head gasket or another engine problem not even related to the cooling system.

Coolant Leaks

Most water pumps have a small hole below the pulley shaft called a weep hole. This hole is intended to allow coolant that has gotten past the seals to leak out. When the pump starts to leak internally, you should be able to notice a small dribble or even a steady flow of coolant coming out. Depending on the seriousness of the situation you might also be able to notice coolant dripping under the vehicle.

Instead of leaking internally, the water pump may also leak externally. Such a situation happens when the water pump gasket cracks and allows coolant to infiltrate between the pump and the engine block. In that case and if you are lucky enough, you might only need to remove the water pump, replace the gasket and that’s it. However, if the pump is driven by the timing belt and considering the considerable amount of time required to remove it, most mechanics would recommend replacing the water pump while you’re there.

Bad water pump leaking

Keep in mind that many of today’s vehicles have plastic pans underneath the engine that can hide leaks or make them seem like they come from a different location. A good word of advice is to periodically check the coolant level and to remove the pans and have a look.

Excessive Noise

A water pump has bearings that keep the shaft stable and allowed the water pump pulley to turn when the engine is running. When these bearings wear out, you might notice a metallic, squeaking or grinding sound coming out of the pulley. It’s important to note that water pump bearing failure also often allows coolant to pass through to the weep hole causing the same kind of symptom as a leaking water pump.

Other pulleys also use bearings, so before jumping to the conclusion and starting to replace the water pump pulley, make sure the sound is actually coming from there first. It’s common for tensioner pulleys and idler pulleys to make a similar noise and the sound will resonate in the front cover making it hard to pinpoint where it’s coming from.

If you are hearing a high-pitched whine or chirp, it is most likely a worn or loose belt problem instead. To make sure it’s coming from the belt, spray some water or brake cleaner on it while the engine is running. If the noise stops temporarily, the problem is belt-related.

Identifying Symptoms of a Bad Water Pump

When signs of a bad water pump appear, the first thing to do is to perform simple checks. There are a few tests you can do to get a good idea of the condition of your car’s water pump. Some of the ways to test a pump are simple and don’t involve removing anything, while other methods require you to disassemble some parts of your engine.

Squeeze Test

Begin this test by starting the engine. You’ll need to wear heat-resistant gloves for this one. If the engine is already at normal operating temperature, squeeze the upper radiator hose as much as possible and release it. You should feel the surge of coolant being pumped through as you release pressure. If you do not feel anything, something is clearly wrong with the water pump. More testing will be required.

Auto mechanic replacing a bad water pump

Surge Test

Start this test with the engine cold. Remove the radiator cap and make sure that the coolant is properly filled. Leave the cap off and start the engine. As the engine warms up, the thermostat will open. As a general rule, you can tell that the thermostat is opened once the upper and lower radiator hoses are both hot. Once it opens, you should be able to see the flow of coolant in the radiator or in the coolant expansion tank. Most of the time, the coolant will look like it ‘s spinning in the radiator. If you can’t see any movement, it means that the pump is not pumping anymore.

Be careful when doing this test. When the coolant in your engine heats up, it expands. In some cases, the coolant might spill out of the radiator. The radiator is also what’s keeping the cooling system pressurized. Positive pressure allows the fluid’s temperature to reach over the boiling point without boiling.  Eventually, without the cap on, the coolant might start boiling and spraying everywhere. If that happens, turn the car off but leave the key in the ON position. That way, the radiator fan can keep turning and cool down the coolant. Wait for the coolant’s temperature to come down, reinstall the cap and wash the front of the car.

Shake Test

For this test, you will need to remove the fan belt that drives your water pump first. This is not a big deal if your vehicle’s water pump is driven by the serpentine but it’s definitely more time consuming if it’s driven by the timing belt.

With the belt removed, grasp the pulley firmly and shake it up and down and back and forth. There should be almost no play. If you can feel the pulley moving, it is a sure sign that the bearings are failing. If it’s the case, you should plan on replacing your water pump in the near future.

Auto mechanic replacing a bad water pump

What Causes a Water Pump to Fail

Water pump failure happens most often when the bearings that hold the shaft wear out. When it happens, the shaft starts to wobble, causing the impeller blade to be less efficient. Bearing noises are one of the most common signs of a bad water pump and shouldn’t be overlooked. Badly worn bearings can even allow the impeller blade to strike the inner surface of the water pump housing causing serious damage. One of the first sign

Many water pumps today use plastic or composite impeller blades. These blades can shatter and cause the water pump to fail. Debris from dirty coolant can accelerate the wear on your water pump. An incorrect water/coolant mix can also cause metal impellers to rust prematurely and significantly reduce their lifespan. To prevent this, it’s a good idea to replace your coolant and flush your cooling system regularly.

In the past, cars traditionally all used the same type of coolant fluid: Prestone green. However, this is not true anymore. Coolant comes in many colors these days. The classic green one is the best-known coolant but long-lasting coolant is usually yellow. Honda’s OEM coolant is blue while Toyota’s is pink. There’s clear universal coolant available. Using the wrong color of coolant in your radiator can create important problems. When in doubt, make sure to check what type of coolant should be used in your owner’s manual.


Bad water pump replacement kit

Water Pump Related Components

When replacing a water pump, and especially if it’s driven by the timing belt, it’s often recommended to replace other components at the same time. It’s already quite time-consuming to remove the timing belt. Consequently, you might as well replace the idler pulley while you’re there. It’s also the perfect moment to inspect the timing belt and the tensioner and replace them if needed. You simply don’t want to reinstall everything back only to have a noisy tensioner problem a week later and having to start over again.

Lukily, water pumps often come in a kit including everything you’ll need. Water pump replacement kit are specifically made based on your car’s timing system configuration. If your car has two idler pulley, the kit will contain two. If your car has some seals that should be replaced, it will be in the kit too. Buying a complete replacement kit is usually the safest way to make sure you fix the problem. It’s also usually much cheaper than buying all the parts separately.

When replacing a water pump, you’ll need to drain the coolant first. When the radiator is empty, you should take a minute to inspect it using a flashlight. If it’s all rusty inside, it might be a good time to replace your radiator too.

In brief

The cooling system on your car is quite a simple one but that doesn’t mean it should be overlooked. Regular maintenance is always your best bet to stay away from coolant problems. However, when it happens, being able to detect the signs of a bad water pump early will help you keep the repair cost as low as possible. If you are not sure of the correct procedure to replace your water pump, get your hands on a copy of your car’s repair manual beforehand. Following the manufacturer’s recommended procedure will significantly speed up the process.

Good luck!


About Derek F

Derek grew up in Southern California and started working on cars when he was a child. He learned from his father and grandfather how to make basic repairs and maintain cars correctly. Derek rebuilt his first engine at 15 years-old, beginning an automotive career that took him to many interesting jobs. Derek has worked as an automotive detailer, managed parts warehouses and auto parts stores, and worked as a mechanic for several years doing brake and suspension work. While pursuing a bachelor’s degree in government journalism, Derek worked for an auto museum where he started to write about cars. Today, Derek uses his expertise gained from many years of practical experience to help educate DIYers and share interesting knowledge about various types of automotive repair and service. Writing about cars helps fund his numerous classic car restoration and customization projects.

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