2000 Yukon Radiator thermostat

[Crystalsilver2000]

My 2000 Yukon is spitting out water but not all the time. I checked the reservoir and when I looked the water seems to be pushing out through the cap of the reservoir. Has anyone had this problem? What could it be? We thought there was air in the radiator so ran in for 5 mins the cap off and no bubbles. The temp on the truck after 5 minutes didn’t move in the dash.