You may have air in the system. Follow this procedure; Turn the heat for the heater setting all the way hot. Wherever the highest point in the cooling system is, that's where it's going to trap the air, and that's where a required bleed point is going to be, but for most vehicles, a radiator, and a radiator cap, is the highest point in the cooling system, and so the radiators can be bled, just simply by removing that cap, and allowing the system to fill up, until all the air is gone. You need to remember also, that there's a thermostat in the system, and when that's sealed, or in the cold or closed position, it can trap air into the bottom side of the engine, so you want to make sure, anytime you're trying to bleed the system, after you've bled it, you've run the engine for at least fifteen, twenty minutes, make sure it's thoroughly warmed up, and the cooling system has cycled several times, and then recheck it after it's cooled, and re-top as necessary, to remove any additional air, that might have been trapped in the engine, so that's how you bleed a radiator, and/or cooling system."
Replace and performa the bleeding procedure again. Try checking the coolant level and then getting air out of the system.
To bleed the cooling system'
Bleed the cooling system by removing the top cap, that lets the air out, and you can add coolant to the radiator, and bleed it out in that fashion. If you need to bleed your cooling system as a unit, that's an entirely different procedure. That outline is going to be given to your owner's manual, and that depends on where the highest point in the cooling system is, as to what the bleeding procedure is, but for a radiator, as long as the cap is the highest point of the radiator. Don't forget to have the heater all the way to hottest setting.
Also, if this does not work, try replacing the radiator cap and possibly the thermostat.