Are all radiator caps the same?

Choosing the right radiator cap can make a big difference

Not all radiator caps are the same. They differ significantly in terms of features, shape, and size − which makes picking the right one for your vehicle very important. 

Are you noticing that your radiator cap isn’t doing its job? A malfunctioning cap may seem harmless, but it can cause plenty of damage to your engine compartment. You may notice:

    • leaking coolant
    • burst or collapsed radiator hoses
    • overheating at lower-than-usual temperatures

And that’s only a few of the problems that might ensue. So, what do you do now? We’ve put together the following guide with everything you need to know about choosing the right radiator cap for your vehicle.

Our team at Natrad are Australia’s trusted auto cooling specialists. We can help with parts and servicing for air conditioners, radiators, and all your vehicle cooling needs. Check out our wide range of radiator caps online.

Radiator caps for pressurised cooling systems

The pressurised cooling system and the radiator pressure cap have been around since the 1940s and have kept vehicles cool for over 80 years. Modern engines tend to require a higher-pressure cooling system compared to their earlier counterparts, which in turn require more effective sealing, i.e. a radiator cap.

The absence of a radiator cap in your cooling system can result in some pretty sticky situations, such as:

      • inefficient cooling
      • loss of coolant
      • overheating

Pressurising the cooling system raises the boiling point of its coolant, which increases the operating temperature range of the coolant, allowing it to withstand higher temperatures without boiling.

This prevents damage from the engine overheating due to a lack of coolant and helps keep the cooling system running smoothly. It also means that manufacturers can build engines with higher operating temperatures, which is especially common in performance vehicles. The radiator cap is a vital part of this process.

What is the function of a radiator cap?

The seal provided by the cap ensures the car’s cooling system remains pressurised and contained as the coolant expands.

Radiator caps can come in several shapes and sizes matched to your car’s radiator. Different vehicles have different cooling systems which operate at particular pressures. Ensuring everything works smoothly comes down to having the right radiator cap for your specific vehicle.

The radiator cap serves other purposes as well, like preventing air from entering the cooling system. If air does enter the system, it can result in engine temperature spikes, overheating and cracking/warping in the part of the engine where air is trapped. 

Finally, the radiator cap allows coolant to go into the expansion recovery tank when it gets hot, and cooling system pressure increases. Once the engine cools, this coolant returns from the recovery tank back into the cooling system. A malfunctioning radiator cap, however, may not hold pressure and cause the engine to overheat at lower-than-expected temperatures or prevent the coolant in the expansion tank from returning to the engine.


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Is the Radiator cap the same as the coolant cap?

It’s important to note that radiator caps and coolant caps are not the same, though they serve related functions in a vehicle’s cooling system. The radiator cap is specifically designed for the radiator and plays a crucial role in regulating pressure within the cooling system. It helps maintain the appropriate pressure to raise the boiling point of the coolant, to prevent overheating. 

On the other hand, the coolant cap (more accurately called the coolant reservoir cap) is located on the coolant reservoir or overflow tank. Its primary function is to maintain the proper level of coolant in the system and allow for the expansion and contraction of coolant as temperatures fluctuate. 

While both caps manage coolant and contribute to the efficiency of the cooling system, they serve distinct purposes in maintaining the overall health and functionality of the vehicle’s engine. 

How to read pressure grading on your radiator cap

A radiator cap will typically have a pressure measurement on it: in either psi or kPa (or both). Psi measures pounds per square inch, and kPa stands for Kilopascals. They are both used to indicate pressure and depend on whether the system uses imperial or metric units of measurement.

Modern radiator caps are designed from 12psi (83kPa) to 30psi (207kPa), with higher cap ratings typically found in performance or industrial applications. When choosing a radiator cap, it’s important you stick with the specified pressure for your system.

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Different seal types in radiator caps

A lot of cooling systems have a coolant recovery system, where coolant flows to and from the expansion tank. These systems require a cap with a double seal to maintain integrity.

Double-seal caps can also be used on non-recovery systems. Non-recovery systems typically have a single seal cap and cannot be used in recovery system applications.

Are all radiator caps the same size?

Radiator cap sizes are not all the same. They come in various sizes and designs to fit the specific requirements of different vehicles. The size of a radiator cap is primarily determined by the radiator neck diameter for the vehicle’s cooling system. 

It’s essential to use a radiator cap that matches the specifications outlined by the vehicle manufacturer to ensure proper sealing and pressure regulation. Using an incorrect cap size or pressure-rated cap can lead to cooling system inefficiencies, potential overheating, and other issues.

What should you look for in a new radiator cap?

To ensure you have the right cap for your vehicle, it’s always a good idea to take a look at what you already have. From there, you can determine the correct size, pressure grading and seal type. Your vehicle’s manual can also tell you the required specifications that your car will need.

Some caps have safety levers on them, usually for performance and mining applications. The lever must be lifted to relieve system pressure prior to opening the cap, which helps prevent scalding and burns.

Find ideal radiator caps at Natrad today

At Natrad, we have a variety of high-quality radiator caps for sale. With 40 years of experience in the industry, we can provide for all your radiator needs at a reasonable price and offer great advice too. 

With a range of recognised brands including Denso, Tridon and Adrad, there’s no compromising on quality when it comes to radiator caps. Speak to a Natrad cooling specialist at your local workshop today.


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