Chrisrt

Hey all, I'm having a wierd problem with my coolant header tank, I've recently had the radiator replaced as it developed a leak, but since having the new radiator fitted now, it reaches 90 and doesn't shown any signs of over heating but when checking the header tank my level goes to minimum when it was showing in-between min and max, if left to cool down and open the header tank it releases air and the coolant goes back to the level in between min and max, any help would be appreciated