2000 Sportsman 400 – STOCK

Engine over heating in slow normal conditions.
Fan was not working so I removed rad, cleaned it
New coolant
Hard wired an new fan in, Fan comes on as soon as the key is on.

Took it for a drive and it overheated again.

What am I missing? Water pump? What is best way to check that without removing it, I know that is a pain…. 🙁

I read something about air in system?