Defective water pump

The coolant pump ensures circulation of coolant in coolant circuit and that engine heat is reliably transmitted to ambient air. At the same time, it is the most strained component of cooling system. Learn on this page how coolant pumps work, what might cause damages and what to take into account during replacement.

The following technical information and practical tips have been compiled by HELLA in order to provide professional support to vehicle workshops in their day-to-day work. The information provided on this website is intended for suitably qualified personnel only.

Water pump

Coolant pumps, also often referred to as water pumps, are mostly powered mechanically via a sprocket or V-ripped belt, and transport the coolant through the engine's coolant circuit . The pumps can be found either directly flanged to the engine or installed at a distance. The designs are very different.

Coolant pumps must withstand enormous temperature variations (- 40°C to ca. +120°C). Changing rotational speeds (500 - 8000 rpm) and pressures of up to 3 bars require great bearing and sealing resistance.

For saving fuel, more electrically powered and electronically controlled coolant pumps will be used in the future.

Operating principle

Drive wheel and impeller are installed on a common shaft. A mechanical seal serves to seal the pump shaft towards the outside. Through the rotary motion of the impeller, coolant is transported within the cooling system. Impellers usually consist of plastic and metal. The bearing strain is lower in plastic wheels. They are at the same time not as liable to cavitation. Plastic wheels will however become brittle over time. The coolant ensures that the mechanical seal is always lubricated and cooled. Due to construction constraints, tiny amounts of coolant can enter the free space behind the sealing ring and exit at the pump's relief bore. The possibly visible coolant traces are not a clear sign of a defective pump.

The design life of a coolant pump is highly dependent on the following factors:

Proper installation.

Care and maintenance of the cooling system.
Coolant quality.
Condition and functional ability of the drive belt and connected auxiliary aggregates.

Electrical coolant pumps

Mechanical coolant pumps directly propelled by the engine continuously transport coolant when that engine is running, even when no cooling is required. Electric coolant pumps and their integrated electronic control, however, are variably activated according to the required cooling needs. They can be used as main, minor or circulating pumps. They operate independent of the engine and as required. The cooling pump does not initially run in case of a cold start. This helps the engine to reach its operating temperature more quickly. Even when idle or after turning off the engine, the electric coolant pump can provide sufficient cooling power since it is not linked to the engine's RPM. This customized engine cooling reduces power consumption and therefore friction losses and fuel consumption. Electric coolant pumps therefore help reduce emissions in modern cooling systems.

An additional advantage consists in the ability to install electric cooling pumps individually and outside of the engine. They are relatively light and maintenance-free, thanks to the brushless installation. At an operating voltage of 12-360 volts, it currently reaches outputs of 15 to 1000 watts. Coolants reduce the temperature of the coolant pump's electric motor. A pulse width-modulated (PWM) signal control makes flexible adjustment possible. This, in turn, enables controlling the transported volume according to the actual needs and independent of engine rotation, thus allowing keeping the cooling temperature constant as required by the respective system. Thanks to their inclusion in the wiring system electronics, electric coolant pumps can also be diagnosed. Depending on the drive type (internal combustion engine, hybrid, electric) and the system, one or even several pumps can be installed in the vehicle.

Electrical coolant pumps have many areas of application:

Engine cooling
Charge air cooling
Cooling of the exhaust gas recirculation
Drive and battery cooling in hybrid and electric vehicles
Transmission cooling
Cooling of diverse power take-offs

Defective water pump

A coolant pump failure can manifest itself as follows:

Noise
Loss of coolant (Fig. 2)
Deficient cooling / Engine overheats

Defective water pump: causes for coolant pump failure — Figure 3

Causes can be:

Mechanical damages:
- Impeller loose / broken
- Lager oder Bearing or seal defective
- Drive wheel damaged
Cross section narrowing due to corrosion or sealant
Cavitation:
- Damage of impeller due to formation or decay of steam bubbles in coolant (Fig. 3)
Electrical damage (short circuit / interruption)

Possible damage symptoms when defective water pump

Water pump defective: damaged drive wheel

Drive wheel damages / loose drive wheel ring:

Strain of timing belt too high
Insufficient orientation of belt

Broken water pump bearing (bearing cage):

Strong vibrations due to defective Visco clutch

Coolant leakage at pump due to E.G.:

Excessive sealant application. Sealant mass residues can enter the cooling circuit and e.g. damage the slide ring seal

Corrosion in entire cooling system:

Defective cylinder head sealing - engine emissions enter cooling system. Negative change of pH value

Water pump defective: damage by pinholing

Pump components such as impeller, housing, slide ring seal and shaft strongly damaged by pinholing:

Expired/Stale coolant with great amount of chlorides (salt compounds) in connection with elevated temperatures.

Water pump leaking: excessive coolant leakage

Excessive leakage of coolant at discharge boring:

Caused by corrosion in cooling system

Replacing water pump

When replacing the coolant pump, always note the instructions of the product package insert and special installation requirements by the vehicle manufacturer. If the cooling system is contaminated, rinse it. You can for example use the HELLA cooling system cleaner.

The cooling system should only be filled with coolants matching the vehicle manufacturer's specifications. Fill and/or ventilate the system according to vehicle manufacturer specifications. A wrong installation can lead to engine overheating , belt drive damage and/or engine damage.

Information on the use, specifications and change intervals of coolants is situated in the respective " Coolant " technical information.

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