Do you happen to have a car made recently (up to 5 years ) by VAG (Audi VW, Skoda and Seat) fitted with either a 1.9 L TDi, 2.0 TDi or
2.0 E engine ? Then read this carefully.
The water pump design was changed by VAG to save some money in a way that could be catastrophic to your engine. It is a volumetric pump so the propeller or fan material is now made of plastic and it is mounted on the shaft through a friction fit.
Any engineer knows that a friction fit between a plastic fan and a steel is not bound to last long. We have obserrved that juste after three years, several pumps start to slip leading to a variety of symptoms that are not pointing necessarily to the pump progressive failure.
VAG has done a terrible design error and they should be ask to change their axis with a grooved one which will then be strong enough.
Having an Audi 80 with a 1.9 TDi which is just a fantastic car with a great engine, I feel that VAG should never make this kind of stupid design error just in order to save a bit of money. Moreover, I would even not accept that error from my students.