After performing any work on the cooling system:

State-of-the-art vehicles have one or more coolant circuits, which divide into different branches, and are closed or released depending on the operating state. In many cases, either several electrical water pumps are installed, or a combination of electrical and switchable mechanical water pumps.

If the system is not vented according to the specifications of the vehicle manufacturer, air can build up in all of these branches and components. This can lead to malfunctions, and in some cases, damage to the components or engine.

When this happens, the risk is not only that the water pumps could run dry. Air bubbles in the system can also impair heat transfer. This can cause heat to build up in some areas (hotspots), which could, for example, directly damage the circuit board of an electrical coolant pump, or cause the electronic components to age prematurely.