Vacuum& electric ally actuated pumps
Unlike e-pumps, the primary water pump on these designs remains beltdriven, but coolant flow is restricted by a movable shroud surrounding the spinning impellor, which is activated by either negative pressure (vacuum) or with a solenoid. Both systems are controlled by the engine ECU. Unlike e-pumps, the rate of coolant flow is not variable on these on/off designs. Vacuum-types can be identified by rubber hoses leading to the pump, perhaps the most widespread application of which can be found with the Volkswagen Group’s 1.2-litre TSI/TFSI (CBZA and CBZB) range of engines, which feature a fail-safe mode so that, should there be zero vacuum, full coolant flow will result and the engine will not overheat.
Some types are operated electrically, and perhaps, the most common type is shown here, used for the Volkswagen Group 1.6-2.0-litre range of diesel engines from 2012. This features a dismountable electric solenoid (the N489) that is attached to the water pump side, which controls an internal mechanism that pushes the shroud over the spinning impellor blades against spring pressure, which provides the fail-safe. We have heard of some replacement pumps not having the internal mechanism, thus not only eliminating potential failures caused by shroud seizure but also, potentially, reducing part costs at the price of higher emissions and fuel consumption. However, the original solenoid must be refitted to the pump, even though it does not do anything, as the internal port is blanked off so that the engine ECU believes that the mechanism is working.