Radiator Cap Buyer's Guide
- A radiator cap, also known as a pressure cap, is more than a seal on your radiator that keeps the coolant in. It functions as a pressure valve that regulates the pressure in your cooling system.
- The radiator cap ensures the cooling system maintains its optimal pressure rating at all times.
- This component contains a spring-loaded valve that is pushed open once a certain amount of pressure has accumulated.
- All radiator caps are made to withstand a specific, predetermined pressure rating.
- Radiator caps can be made out of steel, plastic, aluminum, or metal and rubber.
- The different types of radiator caps are recovery radiator caps, non-recovery radiator caps, and locking radiator caps.
- A radiator cap fails when it no longer fits your vehicle’s required pressure rating or has worn down. A faulty radiator cap may have tears on its gasket that prevent it from properly sealing pressure and coolant into your cooling system.
- When a radiator cap fails, it can lead to engine failure, coolant leaks, and severe damage to parts of your cooling system.
- A radiator cap replacement is priced at anywhere between $10 individually and $250 as part of a cooling fan assembly.
With a properly operating cooling system, your engine is able to function without a hitch, regardless of how cold or hot the weather is outside. This is possible through the many parts of your cooling system working together. However, like all components, most of its parts wear down over time.
One part that is prone to wear but is often overlooked is the radiator cap. Despite being small and barely noticeable, the radiator cap is essential in controlling the pressure in your cooling system. Without it, your engine may overheat, your coolant might leak, and your radiator hose may collapse, resulting in dangerous circumstances and expensive repairs.
In this guide, you’ll learn all about radiator caps, how they work, when to have them replaced, and what to look for in a replacement radiator cap.
What is a radiator cap?
A radiator cap, also known as a pressure cap, is more than just the seal on your radiator that keeps the coolant in. It functions as a pressure valve that regulates the pressure in your cooling system. The radiator cap ensures the cooling system maintains its optimal pressure rating at all times.
Where is the radiator cap? It is attached to your radiator’s neck. The radiator can be found in front of the engine bay. Its exact position varies per vehicle and largely depends on the car’s make and model.
How does a radiator cap work?
A radiator cap regulates the pressure in your cooling system. This component contains a spring-loaded valve that is pushed open once a certain amount of pressure has accumulated. In most modern models, the radiator cap is pressurized.
The radiator cap releases some of the overheated coolant liquid into the overflow tank while your engine is running. As the coolant leaves the system, the pressure that has previously built up drops. Once enough coolant has been let out, the valve closes.
When the engine cools off, the pressure in the cooling system drops significantly, and another smaller valve in the radiator cap opens. This creates a vacuum. The smaller valve sucks back the coolant that was previously expelled in the overflow tank to return to the cooling system.
The set pressure point where the radiator cap opens begins at around 15 pounds per square inch (psi). This can vary depending on the make and model of your vehicle. All radiator caps are made to withstand a specific, predetermined pressure rating.
Types of radiator caps
Radiator caps can be made out of steel, plastic, aluminum, or metal and rubber. The type of radiator cap needed varies depending on the vehicle’s cooling system and the make and model of your car.
Recovery caps (double seal)
The recovery cap is the most common type of radiator cap. It is vented and contains two seals (upper and lower seals) that allow the coolant to flow to and from the recovery expansion tank. This type of cap is used in a full-pressure coolant recovery system.
Non-recovery caps (single seal)
This type of recovery cap is non-vented. It contains a single seal (usually only the lower seal) and is used in an open cooling system. In this type of cooling system, the single seal radiator cap allows the release of overheated coolant and the return of air (instead of coolant) into the system.
Note: While a recovery radiator cap may be used on an open cooling system, a non-recovery radiator cap can’t be used on a recovery cooling system.
Locking radiator caps
This type of radiator cap contains a lever on top. When lifted, this lever allows the safe release of pressure before removing the cap. The locking radiator cap is suitable for both performance and mining applications as it prevents burn accidents from happening before removal.
How does a radiator cap fail?
A radiator cap fails when it has worn down. A faulty radiator cap may have tears on its gasket that prevent it from properly sealing pressure and coolant into your cooling system. When a radiator cap fails, it can lead to engine failure, coolant leaks, and severe damage to parts of your cooling system.
Symptoms of a bad radiator cap
In a coolant recovery system, a bad radiator cap commonly exhibits the following symptoms:
You may notice this leak near your radiator, around the cap itself, on the gaskets, or even on the hoses. This happens when your radiator is stuck or faulty and unable to release excess pressure.
As the radiator cap is essential in maintaining the right pressure in your cooling system, it may cause your engine to overheat once it fails. A bad radiator cap can’t regulate the pressure in your cooling system, therefore failing to cool the engine.
Collapsed radiator hose
When the radiator cap is unable to withstand the pressure, it can lead to under- or over-pressurization. Extremely low pressure within the system creates a vacuum system that could collapse or tear the radiator hose. Extremely high pressure in the system, on the other hand, can damage the hoses. Radiator hoses may also crack under intense pressure.
Instead of releasing just enough coolant to the reservoir, a faulty radiator cap may leak more than the required amount and cause the reservoir to overflow.
A faulty radiator cap can result in low coolant levels. As the coolant evaporates into steam when it overheats, it is not cycled back into the cooling system. A bad radiator cap won’t be able to stop this.
Air inside the cooling system
Lastly, a failed radiator cap will allow air to enter the cooling system. This leads to air pockets in the radiator hoses, thermostat, and even the heater core.
If you notice any of these symptoms on your vehicle, immediately have it checked. When a bad radiator cap is determined to be the cause, consider having it replaced. Keep in mind that replacing a faulty radiator cap can save you from spending on expensive repairs when these problems worsen.
Know the right pressure rating
Cooling systems are designed for a specific pressure level, which varies per make and model. You can't just switch to a lower or higher psi when you look for a replacement. Keep in mind that a radiator cap that doesn’t fit the set pressure rating of your car will not work properly.
How much is a radiator cap?
A radiator cap replacement is priced at anywhere between $10 individually and $250 as part of a cooling fan assembly. The price depends on the type and required pressure rating.
Finding the right fit
When buying a replacement radiator cap, compare it to the factory-installed component. Buy a replacement with a pressure rating that matches your original radiator cap. If you want better performance, consult your owner’s manual and determine if getting a radiator cap with a higher pressure rating is advisable.
Get the right radiator cap for your ride by entering its year, make, and model into our search engine. You can also filter your search according to your preferred brand, price range, finish, shape, and material. Just click search and browse through our selection of heavy-duty radiator caps.
How to Troubleshoot and Fix Your Leaking Radiator Cap
Your car’s temperature control system is able to work efficiently with the help of pressure. Pressure is safely contained in your radiator, thanks to a spring-loaded cap. Overtime, extreme heat and pressure will take its toll on your radiator cap and cause it to wear and get damaged. If the problem is left unchecked, your cap may start to cause a coolant leak, which can eventually lead to engine overheating. Overheating is perhaps every car driver’s worst nightmare; so, to prevent this from happening to you, make sure you address your faulty radiator cap right away. Below are some basic steps that you can follow to easily replace the busted cap in your system.
Difficulty Level: Moderate
Things you’ll need:
- Hand towel
- Coolant system pressure tester
- Replacement radiator cap
Tips and Warnings:
- Never conduct a test to see if your radiator cap is busted when the engine is hot. This can cause you some serious burns.
- For the best results, we recommend that you use an OEM part for your repairs. This will ensure excellent fit and easy installation.
Step 1: Open your hood and put a towel on top of the radiator cap. Start removing the cap by pushing it down and twisting it to the left (counterclockwise).
Step 2: After that, get the pressure tester and screw the cap adapter on it. Once you’ve secured their connection, attach your radiator cap at the other end of the adapter.
Step 3: Next, start running the tester by pumping its handle. Do this until the tester’s gauge registers 15 lbs.
Step 4: Once you’ve stopped pumping, watch the gauge and see if the number starts to drop. If it does, this means you have a busted radiator cap.
Step 5: Throw your old cap and get its replacement. Attach and secure it in place by turning it to the right (clockwise).
Step 6: After tightening it, keep the hood open and start your engine. Check your new cap for any bubbling or discharge while keeping a safe distance from your radiator.