The official start of summer was accompanied by sweltering temperatures across the nation, and what will likely be the first of many heat waves serves as a reminder for drivers to inspect their cooling systems. One small leak in the system can cause your engine to overheat, especially during hot weather. It is especially essential to inspect your vehicle's radiator cap.

How does the radiator cap work?

The name may suggest it is just a lid, but the radiator cap does much more than keep the antifreeze inside the cooling system. The radiator cap is responsible for maintaining pressure in the cooling system, which allows the coolant to flow through the engine and maintain temperatures while you're driving. This part is designed to increase the boiling point of the antifreeze by as much as 45 degrees Fahrenheit. It works much like a pressure cooker. As the coolant heats up, it expands and pressure builds, but a spring-loaded plunger in the radiator cap maintains pressure. When the pressure is too high, the plunger will move and allow coolant to escape the main system and travel to an overflow tank. As the engine cools down, the coolant condenses, creating a vacuum that pulls the antifreeze from the overflow container back into the reservoir.

How can you tell if it's malfunctioning?

Aside from the engine overheating, there are a few telltale signs that can signify the radiator cap is starting to fail. This may be due to the plunger being jammed, which makes it difficult to regulate pressure. When the radiator cap is unable to properly regulate coolant pressure, this can lower the boiling point of the liquid, and you may be able to hear the antifreeze bubbling away. Listen closely after turning off the vehicle for distinct sounds of boiling liquid.

Before you open the hood to get a closer look, make sure you've allowed ample time for the engine to cool off. This can take anywhere from 15 minutes to an hour for a healthy engine, but if your cooling system might be on the fritz, it is best to err on the side of caution and wait a few hours before checking things out. This is especially the case if you suspect the radiator cap may be broken. A faulty cap can leak coolant, which typically reaches very high temperatures when the car is in operation. If this is the case, you may be able to see leaked coolant around the cap edges.

How do you replace the radiator cap?

Replacing a faulty cap is simple. All you have to do is unscrew the old one, purchase a new cap with the same pressure rating and install the new one. When removing the original cap, make sure the engine is completely cool. Otherwise, you risk having hot coolant spray out and burn you as the cooling system releases pressure. Wait a few minutes before screwing the new cap in place to allow the system's pressure to equalize. Then, put the new radiator cap in place, ensuring it is screwed in as tightly as possible. You will need to make sure the new cap is doing its job by starting the engine with the cap in place and watching for signs of leakage around the edges. Make sure you're wearing protective gear and standing at a safe distance just in case.