1989 BMW 525i waterpump testing

I have seen articals identifing 525i as having plastic inpellers that fail. I currently have an overheating problem that I am narrowing down. Thermostat is new and replacing hoses. Tuff job for guys with big arms. I have tried to bleed the system, but all I get is hot air. With temp control to max and temp guage at 12oclock, the rad hoses are hot, but I can not tell if any water is flowing.

How do you verify the water pump is pumping? Goin the trouble of pulling the water pump seems extreme.