Bleeding or flushing an automotive radiator can be done while the radiator is still in the vehicle. Refreshing the coolant will allow debris or dirt to be removed, prolonging the life of the radiator coils. The average backyard mechanic can flush a radiator in about 30 minutes.
Uncap the radiator, and unscrew the radiator drain plug. Normally, this drain plug is located on the inside bottom of the radiator, but models will vary. Once the drain plug is unscrewed, coolant will rush out into the drain pan. If there is not a drain plug, then disconnecting the lower radiator hose will be adequate.
Place the hose at the top inlet for the radiator, and turn on the water at low pressure. This will allow water to continually fill the unit, but with the bottom drain plug open, it will bleed back out. This process can be done with the car running, to flush the entire cooling system, but it is not required to bleed the radiator alone. When the fluid coming out through the drain plug hole is clear for one minute, the radiator is bled completely.
Turn off and disconnect the garden hose, and tighten the drain plug.
Replace the missing coolant with a 50/50 mix of coolant and water, until the radiator is filled. Once full, cap the radiator and add extra coolant to the reservoir tank, usually a white overflow plastic tank located near the radiator cap.
