How to Replace a Radiator Cap

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The radiator serves a very important purpose in your car. It helps to keep the engine cool and is a vital part of the radiator, as it helps to control the flow of coolant and pressure in the system. If your radiator cap becomes damaged or worn out, it can cause serious problems for your car. Luckily, replacing a radiator cap is a very easy process that you can do at home. 

In this article, we’ll show you how to replace a radiator cap in just a few simple steps. 

How Does a Radiator Cap Work?

Stant 10230 Radiator Cap

Before we actually get to replacing the radiator cap, let’s quickly go over how it works. The radiator cap is located on the top of the radiator, and it helps to control the flow of coolant in and out of the radiator. It does this by regulating the pressure in the system. 

As the engine heats up, the coolant expands and creates pressure inside the radiator. This pressure can build up to a point where it could potentially damage the engine. The radiator cap is designed to release this pressure when it gets too high, allowing the coolant to flow back into the radiator and keep the engine safe. 

How to Replace a Radiator Cap


Follow these steps to replace a radiator cap:

Step 1. Allow the Engine to Cool Down

The first step is to allow the engine to cool down completely. You don’t want to be working on a hot engine, as this could be very dangerous. Once the engine is cool, open the hood and locate the radiator cap. Should you try to remove the radiator cap while the engine is hot, you could get seriously burned as the steam and pressure escape. 

Step 2. Remove the Cap

Once the engine is cool, you can remove the radiator cap by unscrewing it. Be careful when doing this, as the pressure inside the radiator will be released. A metal push and turn cap is the most commonly found and is typically round in shape with ears sticking out from each side. To remove this sort of cap, twist the cap counterclockwise while pushing down. 

Step 3. Examine the Cap

Once the cap is removed, take a look at the condition of the gasket. If it looks damaged or worn out, you’ll need to replace it before putting on the new cap. The rubber disc inside the cap is also important, as it helps create a seal. If this is damaged, you’ll need to replace it as well. 

Step 4. Replace the Cap

Now you can replace the radiator cap with a new one. Make sure that you screw it on tight to ensure that there’s no coolant leakage. If you’re not sure how tight to screw it on, consult your car’s manual. 

Common Symptoms of a Bad Radiator Cap

The following are common symptoms of a bad radiator cap:

1. Leaking Coolant

One of the most common symptoms of a bad radiator cap is leaking coolant. If you notice that your coolant level is going down quickly or there’s coolant pooled up under your car, it’s likely that you have a leakage issue. You may also notice dried white streaks on the radiator coming from the cap.

2. Low Coolant

If your radiator cap isn’t sealing properly, it can cause the coolant level in the radiator to drop. Over time, this can lead to engine overheating as the coolant level gets too low. 

Also Read: What happens when Coolant is Low

3. Overflowing Reservoir

If the radiator cap isn’t releasing the pressure like it’s supposed to, it can cause the coolant reservoir to overflow. You’ll likely see coolant pooled up under the hood or on the ground near your car. 

4. Overheating Engine

One of the most serious symptoms of a bad radiator cap is an overheating engine. If the coolant level gets too low, it can cause the engine to overheat. This can lead to serious engine damage if not fixed quickly.

5. Steam from Engine

Another symptom of a bad radiator cap is steam coming from the engine. If you see steam escaping from under the hood, it’s likely that there’s too much pressure in the system. This can be caused by a coolant leak or simply an old and worn-out radiator cap. 

6. White Streak on Radiator

If you notice a white streak(s) on your radiator, it’s likely that the radiator cap is leaking. Over time, the coolant will dry and leave a white residue. This might be an indication that it’s time to replace the radiator cap.

Related Code: P1217 Code – Engine Temperature Condition

Radiator Cap Replacement Cost

The average cost to replace a radiator cap is between $10 and $50. The cost will vary depending on the make and model of your car as well as the type of cap you need. Labor costs will also vary depending on the mechanic and the location as low as $5 or even free.


A radiator cap is a very important part of your car’s cooling system. It helps to maintain the correct amount of pressure in the system and prevents coolant from leaking out.

If your radiator cap is damaged or worn out, it can cause coolant leakage, low coolant levels, overheating, and even engine damage. Be sure to replace it as soon as possible if you suspect that it might be bad.

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