i am 41 yrs old and have spun a wrench or two. I have only seen one water pump that didnt push coolant. It had a plastic impellor that erroded away. I generally replace them due to leaks or as cheap insurance while im there anyways. I personally have never seen a waterpump actually cause overheating. Im not saying it doesnt happen. But I think people blame them way too often. Just my personal opinion.