Problem: How to flush your radiator in your car., Solution: Locate the radiator in back of the engine. Make sure the car is warm and unscrew the radiator cap to let air escape. Unscrew the bleeder valve and drain plug. Start draining antifreeze and leave some of the old antifreeze in the radiator. Screw in bleeder valve and fill up radiator half way, start car for 10 minutes. 