Can I ask how you figured it out as I have just replaced my coolant and am about to do this. I had run my motor for the first time after the change and was waiting for my fan to come on as well, but discovering some oil leaks meant I had to stop the motor.
Did you also run the motor with the radiator cap off as a way of seeing if any air bubbles present?
Yup and that is how I found out, there were some bubbles but I didn't need to add anymore fluid to the system because there was enough in the overflow that it sucked it out from there and cleared out the air pocket.
Make sure you don't forget to blip the throttle a couple times to help circulate the coolant.
Where were the oil leaks coming from?