The radiator cap is a small device that is part of the cooling system on a vehicle. The cap seals off the top of the radiator. But it does more than seal the system. It also functions as a pressure relief valve that regulates the maximum pressure in the system.
An internal combustion engine generates a lot of heat during normal operation. To ensure that your engine operates within a designated heat range without overheating, engine coolant (also known as “antifreeze”) is circulated through the engine block. The coolant absorbs some of the heat, exits the engine, and travels through tiny tubes in the radiator. Air movement across these tubes and their associated cooling fins removes heat from the coolant before it returns to the engine to pick up more heat.
Coolant is able to remove heat more effectively because it is pressurized in the cooling system. The radiator cap ensures that the pressure is able to build without building too high.
Radiator cap replacement is perhaps the simplest service procedure related to the engine cooling system. That said, it can be dangerous or ineffective if not done properly. That is because coolant in the system is extremely hot when the engine is running. Radiator caps are also specific to your engine’s cooling system and are not interchangeable with other vehicles.
Once the correct part has been selected, a technician must allow the engine to cool for about a half an hour to prevent scalding from steaming hot coolant under pressure in the system. From there, the cap is carefully unscrewed (usually with a towel covering the cap) in order to relieve any residual pressure. The new cap is installed and tightened. On some vehicles, the radiator cap might be tricky to access.