Many of today's modern cars utilize a standard water pump to keep their engines at a consistent operating temperature. Their single pump system circulates coolant from the radiator, through the engine block, to a heater core, and then back to the radiator. However, it is common for many vehicles, especially heavy duty pick-ups to have an auxiliary water pump that will expedite the process.

An auxiliary water pump is different than a single water pump in that it is an electrically controlled motor. Its primary use is circulating water by way of a bypass hose from the main coolant lines to a heater core that is used to collect heat and distribute warm air into your vehicle when the heater is turned on. A failing auxiliary water pump will not typically keep you from driving your vehicle, it can definitely affect your comfort in the winter and in severe cold conditions. If not repaired or replaced, it could be dangerous to drive if the pump is failing or has completely failed.

There are a few common warning signs that you should be aware of that might indicate a problem with your auxiliary water pump exists and that it has reached the end of its service life.

1. No warm air is coming from the heater

Since it is the primary job of an auxiliary water pump to supply hot coolant to the heater core, it seems obvious that the first symptom of a problem with this component would be no hot air blowing from the heater. The auxiliary water pump moves hot water or coolant that has recently circulated through the engine block to the heater core. However, when the pump is not working, due to an electronics failure or the motor of the auxiliary pump being broken, the heater core will not be able to heat up. If this does not occur, it's impossible for hot or warm air to enter the cab of your vehicle.

When you turn on the heater and notice that no hot or warm air is blowing into the cab of your car, truck or SUV, you should contact a mechanic to inspect this problem. Note: your engine needs to be at operating temperature in order for the heater core to develop enough heat to blow into your cab. Wait for the engine to warm up before calling the mechanic in this instance.

2. Heater has fluctuating heat

The auxiliary water pump is a consistent flowing device that circulates warm coolant into the heater core – regardless of how fast your engine is running. Because of this fact, if you set a temperature on the thermostat control (if your car has one), it should remain solid. If you notice that the temperature inside your vehicle seems to increase or decrease based on your driving, especially if you notice a temperature decrease when the vehicle is idling, this could be caused by a faulty auxiliary water pump. Contact a mechanic to inspect the water pump or the heater core to see if there is damage to this component.

3. Window defrost is not working

Windows tend to fog up when the temperatures outside are very cold or if there is excess humidity inside of the car. To defog or defrost the windshield, vehicle owners will turn on the windshield defrost button, where warm air from the heater core will blow onto the windshield so you can clearly see outside and drive safe. This application is powered by hot water that is supplied by the auxiliary water pump in many vehicles. If you turn the defroster on and the windows don't defrost rather quickly, it's possible that you have a broken auxiliary water pump.

4. High pitched buzzing sound from under your dashboard

The auxiliary water pump is typically located at the rear of your engine, where the main water line splits to supply the heater core with recently heated coolant. On rare occasions, the auxiliary water pump will experience an electrical problem where the pump runs faster than it should or will continue to run after you've turned the engine off. This is caused by an electrical short in the wiring that powers the auxiliary water pump. The water pump will make a high pitched buzzing sound if this occurs.

If you recognize any of the above warning signs or symptoms, contact your local ASE certified mechanic as soon as possible so they can inspect the problem and replace your auxiliary water pump if needed.

This article originally appeared on YourMechanic.com as Symptoms of a Bad or Failing Water Pump (Auxiliary) and was authored by Timothy Charlet.


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