Is there damage or not?
If coolant agent is visible on the outside of the water pump, this does not usually indicate damage. Instead, it is a result of the water pumps being equipped with a special gasket system on the rotating shaft. The cooling system is sealed on the shaft with a sliding ring seal. This gasket consists of a fixed part and a rotating part. A spring compresses the two parts, to keep the cooling system sealed even when in an unpressurised state. Both of the sliding ring’s contact surfaces are lubricated and cooled together using the cooling liquid. This type of construction automatically causes small quantities of coolant agent to repeatedly leak through the contact surfaces. As a result, a small amount of cooling liquid or coloured deposits may become visible on the leakage hole or outer face of the water pump. This can lead to confusion, in particular after installation during the leak test. However, a certain amount of leakage is normal, and not a cause for concern.
Replacing the coolant agent
However, if larger quantities of the coolant agent leak through the sliding ring seal over longer periods of time, and therefore also escape via the leakage hole, this is usually caused by impurities in the coolant agent. This is because if the cooling system is not cleaned when the pump is changed, or if contaminated coolant agent is used, lime, rust and dirt can cause increased wear of the contact surfaces, leading to coolant leakage. To prevent this, it is absolutely necessary to make sure that the specified change intervals of the coolant agent are adhered to.