For info only after a discussion with my local mechanic ...

Mechanic told me that he has had several overheating 1.9tdi VAG engines present to him lately with strange symptoms; ok no problems at tickover, then overheating when being driven ... the opposite of what you would expect?

The solution was water pump related; when at tickover the brass pin in the middle nof the impeller grips and the pump works ok, at anything over tickover that grip is lost and the car overheats, and then returns to normal again at tickover.

Anyone experiencing similar problems?

I wonder how many miles are on these engines? It's certainly considered best practice on the old 1.8Ts to replace the waterpump at the same time as the cambelt (60k / 4 years), however whether this is necessary on other engines is less clear. Having a grasp on the age / mileage of these engines with failed waterpumps would be useful to see whether advice on changes should be like on the 1.8T, or every other cambelt change, or what...