The Pontiac Sunfire was introduced in 1995. The Sunfire was equipped with two different engine options: the 2.2-liter inline 4-cylinder, or a 2.4-liter inline 4-cylinder. The cooling system in the Sunfire engine can collect air pockets when certain parts of the cooling system are replaced, such as the water pump, thermostat, or radiator hoses. Coolant that falls out of these parts does not automatically get replaced with coolant when you reinstall them. The cooling system breathing process is one of heating the system without pressurizing the system. The heated cooling system will force the air pockets to the top and out of the cooling system, as the air pockets weigh less than the coolant.
Open the hood on your Sunfire. Remove the radiator cap from the radiator overflow bottle.
Turn the engine on in the Sunfire, and let the engine run for no less than 15 minutes. Set the dials on the heater control panel to full fan speed, full heat, and front defrost positions. This will speed up the processes of heating the engine to full temperature. Removing the radiator cap and performing these procedures will allow the pressure in the engine to build up. As the pressure gradually increases, the weight of the coolant will force air bubbles out through the radiator overflow bottle hole. This process is called bleeding the cooling system.
Turn the engine off when you notice that there are no more bubbles coming from the radiator overflow. Top off the radiator overflow bottle with fresh coolant. Use 50/50 diluted, universal coolant to fill the overflow. Replace the radiator cap when the reservoir is at the "Full" mark.
