Diagnosing a Water Pump Failure

Updated on October 8, 2016
If your water pump leaks and contaminates the timing belt, repalce both.
If your water pump leaks and contaminates the timing belt, repalce both. | Source

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.

I. How a Water Pump Works
Five Main Reasons Your Water Pump Fails
What You Should Know About Bad Water Pump Symptoms
II. Testing a Bad Water Pump
A) Diagnosing Water Pump Operation
B) Diagnosing Bearing Failure
C) Diagnosing Seal Failure
What If Your Water Pump is OK but The Engine Still Overheats?
Top 5 Tips to Increase Water Pump Service Life

I. 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. | Source

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 prevents your 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.

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 will usually show up on the floor right under the water pump.
  • 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.

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

A clogged radiator will prevent coolant circulation.
A clogged radiator will prevent coolant circulation. | Source

II. 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.

A) Diagnosing Water Pump Operation

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

  1. First, place your transmission in Park (automatic) or Neutral (manual) and apply the Parking brakes.
  2. First, 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. | Source

B) 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. It 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.

C) 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. | Source

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.
  • 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.
  2. 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.
  3. Fix engine overheating problems as soon as possible. Overheating will damage the seal and impeller inside the water pump.
  4. Use a quality water pump to keep your cooling system working at optimal condition for a longer period.
  5. 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 brake 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.

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.

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