Put the UTV with the front end up at a 45 deg angle and loosen the cap with the engine running and run the engine and rev it up every so often for 10 to 15 minutes. This will remove trapped air in the engine and the system. Also check to make sure the radiator is clear and the fan is coming on also make sure after it is warmed up that there is flow in the radiator if if there is no flow you need to test or change out the thermostat.....