Coolant Bleeder Screw

What is a Coolant Bleeder Screw?

The coolant bleeder screw, also known as a coolant air bleeder valve or purge valve, is often a plastic screw or valve that is designed to remove air pockets or trapped air bubbles in the engine's cooling system for optimal coolant pressure and flow. A vehicle's coolant bleeder screw is usually located at the highest point of the cooling system, and may be built into a bleed housing assembly to allow you to bleed the cooling system after coolant flushes or repairs. During the process of flushing or refilling the cooling system, air can become trapped and create bubbles or pockets in the coolant. These air pockets can hinder the circulation of coolant, leading to inefficient cooling and potential overheating. Air also heats up more quickly than coolant, which can cause hot spots in the engine or erratic temperature gauge operation. The coolant bleeder screw provides a way to release these air bubbles, allowing the cooling system to function optimally. To use the coolant bleeder screw, the engine should be off and cool to the touch. The radiator or coolant reservoir cap typically needs to be removed during this procedure, and the bleeder screw gently opened. As the air is released, coolant will begin to flow out of the bleeder screw. Once a stream of coolant without air bubbles is observed, the bleeder screw can be closed. In some cases, the bleeder screw can be broken, damaged, or become stuck, preventing you from properly bleeding the cooling system. Air trapped in the cooling system can quickly lead to overheating or poor cooling performance, and a damaged or leaking bleeder screw or valve should be replaced at the first sign of a problem. If you need a new bleeder screw, wrenches, or pliers, shop O'Reilly Auto Parts selection of replacement coolant bleeder screws for a complete repair. You can also learn more about how to flush and fill your cooling system with our helpful How-To Hub resources.