What Are The Signs Of A Bad Radiator Cap?

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One component that many drivers pay little attention to is the radiator cap. When you open the hood, you will find this cap on top of the radiator in front of the engine compartment.

Although seemingly a small part, this radiator cap plays a rather important role. In this article, we will explain the role of the radiator cap, the need to replace it, and when to do so.

What Is The Role Of A Car Radiator & Radiator Cap?

The radiator plays an important role in cooling the heat generated by the engine and preventing overheating.

The way it works is that coolant cooled by the radiator is sent to the engine, removes heat from the engine, returns to the radiator, is cooled again, and circulates back to the engine.

Many people think of the cap on the radiator as just a plug, but in fact, this cap plays a very important role. To be more specific, it plays the role of three valves: a sealing valve, a pressurizing valve, and a negative pressure valve.

Each of these valves performs the following functions.

Sealed Valve

As the name suggests, this valve seals the radiator to prevent coolant from leaking out.

Pressurizing Valve

As the temperature of the cooling water rises and expands, the pressure in the radiator rises and the boiling point of the cooling water also rises (approx. 120°C).

The increased boiling point allows the cooling water to function at temperatures above 100°C, making it less likely to overheat. In the unlikely event that the coolant boils, the increased volume and pressure will damage the radiator body and pathways.

Therefore, if the pressure exceeds the set pressure, the pressurizing valve on the radiator cap opens to release excess pressure (coolant) into the reservoir tank.

Negative Pressure Valve

Pressure (coolant) is released to the reservoir tank, and when the temperature drops, the pressure inside the radiator also drops. If the pressure inside the radiator remains negative, there is a risk of damage to the radiator.

Therefore, when the pressure becomes negative, the negative pressure valve on the radiator cap opens to return cooling water from the reservoir tank, thereby adjusting the pressure.

Does The Radiator Cap Need To Be Replaced? What Are The Effects Of Deterioration?

Radiator caps are different from ordinary plugs because they play three roles: sealing valve, pressurizing valve, and negative pressure valve, and they are easily damaged or deteriorated.

In particular, since spring is used as a component when this spring deteriorates, it often does not work properly. If the radiator cap is damaged, it will not be able to control pressure properly, and overheating is likely to occur.

In addition to visible abnormalities such as rust and deformation, if you suspect that the radiator cap is abnormal based on symptoms such as increased coolant temperature or decreased coolant flow, you should have it inspected at a service shop, or specialty store, or dealer.

Of course, if there is an abnormality, it should be replaced.

Although radiator caps are consumable items and can be replaced by yourself, we recommend that you bring your car to a maintenance shop or other facility for replacement as much as possible, including which cap to use, due to differences in characteristics and materials.