Make sure you don't have the reservoir cap, which is the pressure cap in the system, mixed with the radiator cap, which will NOT have a plunger nor spring on the bottom of it. Top off the radiator and install the cap. Fill the coolant level in the reservoir to the "MAX" line on the side of it. Jack the front of the vehicle up as high as you safely can...or, drive the front wheels on a set of ramps or park on a steep hill (nose forward). Start the engine and set the front and, if applies, rear heater to the hottest temperature setting. Run the engine at 2500-3000 RPM for at least 10-minutes, or longer as necessary until hot (approx. 140 degrees F.) air comes out of the heater vents. When done, shut the engine off and lower the vehicle. Any air should be purged from the system. When the engine is cold, top off the radiator and reservoir as necessary.