Set the heater controls to the maximum heat setting, then start the engine. Let the engine idle until it reaches operating temperature and the thermostat opens. Have a helper increase the engine speed and hold it at 2,500 rpm for 30 seconds. Watch the coolant level and continue to top it off as needed. If the engine begins to overheat, shut it down, wait for it to cool and start this section again. You have cleared the air out of the system when the coolant level holds steady and the heater blows hot air. Install the radiator cap and shut off the engine. Lower the vehicle to the ground.