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Diagnosing a Water Pump Failure

Dan Ferrell writes about DIY car maintenance and repair. He has certifications in Automation and Control Technology and Technical Writing.

If your water pump leaks and contaminates the timing belt, repalce both.

If your water pump leaks and contaminates the timing belt, repalce both.

Diagnosing a Failed Water Pump Can Be Tricky

Diagnosing a water pump failure is one of those dreadful repair tasks most car drivers don't like to find themselves in.

First, taking your car to the shop isn't going to be cheap and trying to find out on your own if your water pump has failed isn't much fun either. And that's because potential clues can lead you astray. You start replacing components that don't fix anything.

However, your real problem here is that applying the wrong fixes can get real expensive pretty soon. And dangerous.

Give it a chance, and a bad water pump will overheat and destroy your engine in no time.

But things don't have to get to that point. A failed water pump will give you specific clues that something is amiss, if you know how to look for them.

This guide outlines, in a step-by-step way, three different but related methods you can use now to help you check and confirm that your water pump in your car has failed. Most of the time you won't need any tools unless you must remove components to gain access to your pump. Sometimes, though, a special tool will prove valuable in certain situations (we'll get to it later), but often it is not needed.

Before getting into the steps, let's take a look at the configuration and operation of a common car water pump. This will help in diagnosing yours.


1. How a Water Pump Works

Five Main Reasons Your Water Pump Fails

What You Should Know About Bad Water Pump Symptoms

2. Testing a Bad Water Pump

Diagnosing Water Pump Operation

Diagnosing Bearing Failure

Diagnosing Seal Failure

What If Your Water Pump Is OK but The Engine Still Overheats?

Top 5 Tips to Increase Water Pump Service Life

1. How a Water Pump Works

Your car water pump has a simple but efficient design. The pump uses an impeller, mounted on one end of a centered shaft, to push coolant throughout your engine, cylinder head, radiator, heater core, intake manifold, connecting hoses and lines.

The centered shaft has a pulley on the other end and is supported by one or two bearings to transfer rotating force to the impeller.

Depending on your particular vehicle make and model, your engine may use a serpentine belt, drive belt, or timing belt to run your water pump.

Although a shaft seal isolates coolant from the bearing assembly, your water pump silver housing has a weep hole (or relief port) to one side or at the bottom to allow coolant to exit if your pump develops a leak.

A bad water pump can overheat your engine.

A bad water pump can overheat your engine.

Five Main Reasons Your Water Pump Fails

A water pump may fail in more than one way. For example:

  • An old, worn out seal starts leaking coolant.
  • An over-tensed belt puts extra pressure on the shaft and bearing, which may lead to a broken shaft or bearing, and a leak.
  • A worn out or damaged bearing or impeller prevents your water pump from properly rotating or at all, causing your engine to overheat.
  • Old coolant and rust buildup destroy your water pump.
  • An old gasket gives in and leaks.
  • Bad seal. A faulty installation that fails to seal the water pump properly is the main cause of premature failure.
  • Low system pressure (bad radiator cap, low fluid level, collapsed hose, clogging radiator) can cause water pump cavitation and failure.

What You Should Know About Bad Water Pump Symptoms

A failed water pump shares some symptoms with other bad components in your vehicle:

  • Coolant leak. A bad hose, gasket or radiator may also leak coolant. But the water pump glossy, green leak (or whatever the color of your coolant is) will usually show up on the floor right under the water pump or close to it.
  • Engine overheating. Also, a stuck thermostat or clogged radiator will cause your engine to overheat.
  • A whining, sometimes a grinding, noise coming from the front of your engine. A bad accessory pulley, slipping or misaligned belt can become noisy, as well.
  • Coolant warmer than normal during the hot summer months.
  • Not much heat coming out of the heater during the winter, accompanied by low coolant level.

Since these symptoms may appear when other components go bad as well, you still need to confirm the failure of your pump.

A clogged radiator will prevent coolant circulation.

A clogged radiator will prevent coolant circulation.

2. Testing a Bad Water Pump

When testing for a bad water pump becomes difficult, you can divide your diagnostic into three simple procedures that give you a better chance of revealing the fault and the type of failure you are facing.

The advantage with this approach is that your diagnostic can make it easier to tell whether other components played a role in your water pump failure, which you must correct before installing a new pump.

So first, we'll check the operation of your water pump, followed by a diagnostic of the bearing, and signs of a potential water pump seal failure. You can combine one or more of these methods until you can verify the failure and possibly pinpoint the cause.

Diagnosing Water Pump Operation

The purpose of this type of diagnostic is to check whether your water pump is working.

  1. Place your transmission in Park (automatic) or Neutral (manual) and apply the parking brakes.
  2. Remove the radiator cap and start the engine.
  3. Let your engine idle for about 15 to 20 minutes to let it reach operating temperature.
  4. At operating temperature, you should see through the radiator opening how the coolant begins to circulate; otherwise, either your thermostat has failed to open, the radiator is clogged, or your water pump isn't working.
  5. If you suspect the water pump isn't working, replace the radiator cap and, using a shop rag to prevent burning your hand, squeeze the upper radiator hose (the one going from the radiator to the engine).
  6. With a working water pump, you should feel the surge of coolant as you release the radiator hose.
  7. When you don't feel the surge of coolant, squeeze the upper radiator hose again, and while an assistant depresses the accelerator to increase engine speed, release the radiator hose.
  8. If you still don't feel the surge of coolant through the upper radiator hose, most likely coolant is not circulating. Get inside the passenger compartment.
  9. With the engine still idling, turn on the heater to Max.
  10. If you feel very little heat or no heat coming out, and you've noticed your engine overheating, you'll need to locate the fault among a stuck-closed thermostat, a clogged radiator, and a failed water pump. Go on to the next procedure.
A sutck closed thermostat will block coolant circulation and overheat the engine, as well.

A sutck closed thermostat will block coolant circulation and overheat the engine, as well.

Diagnosing Water Pump Bearing Failure

One way to check for worn out or failed pump bearing is to check for water pump shaft movement.

1. With a faulty bearing, you can often hear a squealing, howling, or sometimes a grinding noise coming from the front of the engine. Even if you don't hear any noises, apply the next steps.

  • To isolate the source of the noise, you can use a large screwdriver or a length of rubber hose to isolate the source.
  • Start your engine. Keep your hands and screwdriver or hose away from moving parts.
  • Touch the front of your water pump housing with the tip of the screwdriver shaft or one end of the hose.
  • Put the other end of the screwdriver or hose against your ear. If the bearings are worn out or damaged, you'll clearly hear the noise coming from your water pump as the bearing causes a rough rotation of the pump shaft.

Be aware that a loose or slipping drive belt, an AC compressor, alternator, steering pump, belt tensioner, or another accessory driven by the belt may also cause a squealing noise.

2. Check the water pump shaft and pulley for signs of damage or movement.

On vehicle models where a serpentine, drive or timing belt runs the water pump, you may need to remove the belt to manually check the water pump pulley.

  • Wiggle your pump pulley with your hand. If you notice damage or movement, replace the water pump.
  • Rotate the pulley by hand. It should turn freely but not feel loose or rough; otherwise, replace the pump.
  • On vehicles where the radiator fan attaches to the water pump assembly, you can grab the fan and carefully wiggle the fan. If you notice movement, most likely the water pump will need replacing, but check that all mounting bolts are tight. And carefully examine the fan as well. With enough time, a loose or damaged fan will cause the water pump to fail.

Diagnosing Water Pump Seal Failure

A bad seal will cause the water pump to fail, allowing coolant to leak. Often, a simple visual inspection of the water pump itself can reveal the leak of a seal or even a gasket.

  1. On some vehicle models, you have easy access to the pump for inspection. On other models, you may need to remove an engine front cover to gain access and even raise the vehicle and supporting it on jack stands.
  2. Once you gain access to your pump, use a flashlight to inspect the pump. Check the pump weep or relief port (at the bottom, to one side, or under the pulley), around the shaft or pulley and mounting area (where the pump comes in contact with the engine block)
  3. Also, look where the radiator hose attaches to the water pump.
  4. Look for traces of coolant residue or tracks of dried coolant. If your water pump is driven by a drive or serpentine belt and you find traces of coolant, make sure the leak is not coming from an over-head hose or another source above the water pump.

A slightly wet weep hole isn't cause for concern. However, a dripping weep hole means a failed shaft seal.

If your timing belt runs the water pump, it's a good idea to replace the belt at the same time.

If your timing belt runs the water pump, it's a good idea to replace the belt at the same time.

I Found Traces of a Leak but Don't Know the Source

If you find traces of a coolant leak around your water pump but aren't sure of its source, pressure test the cooling system:

  1. Get a hand pressure tester. You may loan a tester from your local auto parts store. This is a simple hand-operated air pump.
  2. With the engine off, install the tester cap in place of your radiator cap and start pressurizing the system by squeezing the pump handle.
  3. The pump comes with a gauge so you know how much pressure you're applying. Do not exceed the pressure your cooling system is rated for—about 14 or 15 psi (check your radiator cap or your vehicle repair manual, if necessary).
  4. With your system pressurized, make a visual inspection of the water pump. Look around the weep hole, shaft, pulley, mounting surface and hoses above the water pump.

If you discover a small leak at the pump, don't try to fix it with an after market sealer. Most likely the problem will come back or you won't be able to repair it successfully.

What if My Water Pump Is OK but The Engine Still Overheats?

Other than a failed water pump, you can find several reasons behind an overheating engine you might want to check:

  • Make sure the cooling system has enough coolant. Check coolant level at the coolant overflow tank.
  • If your water pump is run by a belt, check that your drive belt or serpentine belt is not loose; a loose belt will not allow the water pump impeller to push coolant at the proper rate, causing your engine to overheat.
  • Check for a stuck-closed thermostat. A failed thermostat in the closed position will not allow coolant to flow into the radiator.
  • Make sure your radiator is not clogged. A clogged radiator will prevent coolant circulation.
  • Also, remove leaves, bugs and debris restricting air flow around radiator fins.
  • Bad radiator fan. There won't be enough airflow through the radiator to remove heat from hot coolant.
  • Bad radiator cap, worn out or damaged seal. A failed cap will lower coolant boiling point.
  • Air in the cooling system. Air may form pockets (bubbles) that prevent coolant from removing heat away from the engine.

Top 5 Tips to Increase Water Pump Service Life

A water pump often fails prematurely. You can avoid this by following some simple guidelines:

  1. Replace old coolant at the recommended car manufacturer service interval. Old, worn out coolant allows rust to build up causing your water pump and other cooling system parts to fail. And only use the correct antifreeze for your application. Consult your car owner's manual or vehicle repair manual.
  2. Before installing a new pump, hold the pump with the impeller side up. Pour some new coolant over the impeller side of the pump and rotate the pump's pulley 10 time. This will create a mechanical seal for the pump after installation. You may see a bit of coolant seepage through the weep hole during pump operation but it'll stop after the mechanical seal has formed. And it's recommended to replace the belt and tensioner when installing a new pump.
  3. When replacing a belt that runs the water pump, install the belt with the appropriate tension and replace belts at the recommended car manufacturer schedule (including belt tensioner), and verify the belt aligns with all the pulleys it runs. A loose, misaligned, or over tensed belt will prevent proper operation of the water pump and other accessories and can damage the pump shaft, bearing and seal.
  4. Fix engine overheating problems as soon as possible. Overheating will damage the seal and impeller inside the water pump.
  5. Use a quality water pump to keep your cooling system working at optimal condition for a longer period.
  6. When replacing a water pump run by a timing belt, always replace the timing belt at the same time, especially if the water pump was leaking. A coolant contaminated timing belt will have a reduced service life. On the other hand, a worn out timing belt may break and damage your new water pump. In most applications, the water pump and timing belt have about the same service life period (50,000 miles or more), so you'll save time and money by doing both at the same time.
  7. When replacing the water pump, follow the manufacturer's installation instructions, or consult your vehicle repair manuals. Most water pumps fail prematurely because of improperly sealed.

Final Thoughts

You should begin diagnosing a water pump failure as soon as you suspect something is wrong. Apply the three methods outlined in this simple guide. An early diagnostic can save you thousands of dollars in repairs. Remember that driving a car with a failed water pump can leave you stranded in the middle of the road, with an overheated engine and a much more expensive repair.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: My car doesn't start getting hot immediately, but the temperature goes up after driving for a while. Would this be the thermostat sticking?

Answer: This is the most common reason. Check also the cooling make sure it's not constantly running. If necessary, check the temperature sensor.

Question: I've already replaced the cap and thermostat of my water pump. It still builds up so much pressure that most of the coolant is pushed out of the radiator and into the overflow tank. Before driving, I have to take off cap to release pressure and let coolant drain back into the radiator. Would a clogged radiator most likely be the issue?

Answer: There are three things you might want to check. Make sure you have the correct cap for your application, see your vehicle repair manual, if necessary. Also, make sure the cap is sealing correctly. Closely inspect the radiator neck for damage or anything in there not allowing the cap to seal properly. Then, check for a blown head gasket leaking hydrocarbons into the cooling system. This will require a leak down test.

Question: I have a 2007 Nissan Pathfinder. The temperature rises the faster you drive unless I run the heat at full blast. But I can put the vehicle in park, run the AC, and it never overheats. What would cause that?

Answer: There are several problems that could cause this. Debris and bugs can cause insufficient air flow through the radiator. Also, the radiator may be partially restricted. If the cooling fan isn't working properly, this may cause the same problem. Take a look at the lower and upper radiator hoses. If a hose is collapsing when engine speed increases, it will restrict coolant flow. Running the AC at full blast help to lower the coolant temperature.

Question: If my coolant leaks out almost completely when I fill the reservoir how do I know for sure it's the water pump and not something else before paying for the part? I'm not a mechanic, but I changed the reservoir and hoses. Also replaced the AC fan assembly. Now I have this problem. Please help.

Answer: Take a close look at the pump. If the pump is leaking, you should be able to see traces of coolant around the pump. You can try listening to the pump with the engine at idle (be very careful with moving components) using a piece of hose. Put one end of the hose against the pump and the other end at your ear. You may be able to hear a whirring noise if the pump bearings are worn or have failed. If not, look around the cooling system for the leak. You shouldn't replace components until you know what is causing the leak. Small leaks are hard to find sometimes.

Question: After turning a water pump on, the engine check light came on, and it misfired. Why is this?

Answer: Make sure that you purged the system correctly. You need to get rid of all the air pockets in there. Otherwise, that could cause overheat, misfire and hence the CEL. Download the codes and see what they say.

Question: can coolant leak from the radiator hose cause water pump failure?

Answer: Not really, the water pump is sealed. These pumps have a weep hole where coolant leaks through when the bearing or seal fail.

Question: Why does my car's fan run on high at times?

Answer: If your vehicle uses a clutch fan, check the clutch; otherwise, there could be a problem with an AC compressor pressure switch.

Question: The water pump gave up on my ‘05 Toyota Sienna, and I have noticed that the upper front timing cover was cracked. Also found out that half of the timing belt is off the top sprocket and will not move at all. Is that normal for a car when that happens to the water pump?

Answer: If the water pump sprocket seized, it probably affected the timing belt and caused a misalignment. When changing the water pump, have the mechanic check the sprockets, idler and adjuster and install a new belt. Install a new timing belt kit would be the best way to go.

Question: My car overheats but runs well. It doesn't overheat until the coolant runs out, which happens every time after going about 3 or 4 miles (6.44 km) if that. What would cause my car's coolant to be gone so fast? The heat does work. It may get 1 out of 7 drives/rides.

Answer: There's a leak in the system you need to find. If you don't see any signs of leakage on the ground where you park your car, it could be an internal leak. This other post may help:

Question: Why is my water pump getting hot?

Answer: If the temperature gauge indicates the engine is overheating, the water pump bearing may be faulty and not allowing coolant to circulate properly. Another possibility is the thermostat is not functioning right. Depending on your particular model, you can try to listen to the pump with a length of hose. Put one end against the water pump and the other end at your ear and see if you hear noise coming from the pump. This other post can help you check your thermostat.

Question: Does it sound normal or appropriate for the water pump inside the intake to be a 13 hour job, and cost around $1330?

Answer: A repair job for a particular component can vary by hundreds of dollars, depending on your particular model and the cost for the part for the particular model. But you can get an estimate through several online sites like this:

There are other ones. You can check more than one. Just search for "car repair estimate" and you'll get a list of several sites. Hope this helps.

Question: My car's water leaks more when the engine is hot. Could this be caused by a damaged water pump or are the seals out?

Answer: It could be the water pump or another cooling system component. Sometimes, exterior leaks are easy to find. If possible, follow the leak marks left on the engine. You may need to raise your vehicle and support it on jack stands. This other post has some common parts that may eventually leak: