On-demand water pumps
Common types you’ll encounter.
Used on electric and hybrid vehicles to cool their high-voltage inverters, e-pumps are also used on conventional combustion engines. Being controlled by the engine ECU means that a more accurate and narrower temperature range is maintained. Being independent of engine speed, the pump’s RPM can not only be varied, but it can also be switched off after a cold start and activated again after the engine has shut down, to disperse hotspots. The lack of a belt drive reduces mechanical drag and, as a result, CO2 output.
Many e-pump faults are the same as those of conventional types. Impellors can become detached from their shafts and corrosion can form due to incorrect coolant being used, or drain intervals being exceeded. However, one new issue that has arisen is that the pump’s internal circuit board components can corrode and fail due to condensation, caused by repeated engine heating and cooling cycles. Damage and corrosion to electrical connectors also prevent the pump from functioning.
Being controlled electrically, most of these pumps boast self-diagnostic capabilities and problems with them should generate fault codes in the engine ECU – look for these and the frequencies at which they occur. Faults includes pump impellor speed deviation, or restriction of impellor movement, leading to an increase in current draw. When driving, any dashboard warning must be noted, as should any abnormal temperature gauge activity. Listen for unusual noises from under the bonnet, particularly after the engine has stopped and the pump remains active.
Using diagnostic equipment, activate the pump manually (although some cars do not need diagnostics to switch the pump on temporarily) by running it at varying speeds and note that pressure builds within the cooling system – such as hoses pressurising, or coolant flowing through the expansion tank, depending on model. Do not forget to check the live data readings. Inspect the electrical circuits and wiring using a multimeter and the appropriate data for your make/model.
If replacing the pump, research if a kit of parts is available that may include new fixings (some bolts on certain BMWS are stretch types and must not be refitted, for example), plus relevant sensors, thermostat, pipes, clips and hoses.