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Bad Radiator Cap: Signs You Might Need to Invest in a New One

How To Know If Radiator Cap Is Bad

Are you familiar with all of the different parts that are in your car’s cooling system? If you’re not, you should get familiar with as many of them as you can since they play a vital role in preventing your car’s engine from overheating. From the radiator and the coolant expansion tank to the water pump and the heater core, they’re all very important in the grand scheme of things. Even something seemingly as simple as your radiator cap has an essential job that helps keep your engine cooler than it would be otherwise. It’s why you need to avoid driving your car around with a bad radiator cap in it. Let’s learn more about what a radiator cap is before talking about some of the signs that you’ll see when you have a bad radiator cap on your hands.

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What Is a Radiator Cap?

In a few moments, we’re going to discuss what might cause a bad radiator cap in your car, how you can spot problems with your car’s radiator cap, and what you can do to replace a radiator cap. But before we get into all of that, it’s important for us to talk about what a radiator cap is. It’ll help you understand why you shouldn’t ever attempt to drive your car with a bad radiator cap in it.


The radiator cap in your car is actually one of the first things that you’ll see when you pop the hood on your vehicle and look under it. It sits right on top of your radiator, and when you open it up, you’ll find that it has a spring-loaded plunger in it. You can easily take the radiator cap in your car off when your car’s engine is cold so that you can check to see how much coolant you have in your car. You can add coolant to your car when the radiator cap is removed.

Why Is a Radiator Cap Important?

The radiator cap in your car is important, first and foremost, because it obviously keeps the coolant in your car flowing smoothly through your system. It’s also important because it makes it nice and convenient for you to add coolant to your car when it’s running low on it. But those aren’t the only reasons why the radiator cap in your car is important. There is another big reason why you want to keep your radiator cap in good working order and not drive around with a bad radiator cap.


In addition to keeping the coolant in your car contained, the radiator cap in your car is also responsible for keeping your car’s entire cooling system pressurized. The pressure in this system is what allows the boiling point of your car’s coolant to be elevated, which makes it possible for it to remove heat from your engine and keep it cool. But at the same time, if you have too much pressure in this system, it can cause damage to occur to certain components, and it can even cause coolant to leak in some cases.


Your radiator cap prevents these things from happening by releasing any excess pressure that builds up in your cooling system. Anytime there is too much pressure in your system, the radiator cap will push it in the direction of your expansion tank. But it won’t be able to do this if you have a bad radiator cap in your car. You need to replace a bad radiator cap immediately to stop it from taking a toll on your cooling system as a whole.

How Long Should a Radiator Cap Last?

Even though the radiator cap in your car is a relatively simple and straightforward part that doesn’t seem like it would break down on you very often, it’s a part that is almost constantly under pressure. As a result, it’s a part that is going to break down on you at some point in time. It’s all just a matter of when that will happen, and it can be difficult to predict it. While some radiator caps will last for the entire time a person has a car, others will give out on you when you push them too hard and need to be replaced.


It’s not uncommon for a radiator cap to go bad by cracking or hardening over time. When a radiator cap is put to the test day after day, it’ll eventually give out on you and need to be replaced. There are also seals around a radiator cap that can go bad over the years. When the seals on radiator caps go bad, you’ll have no choice but to replace them. Additionally, the spring, plunger, and valves that are situated inside of a radiator cap can all go bad and stop a radiator cap from being able to maintain the pressure in a cooling system properly.


As we just alluded to, there is really no telling when any of these things might happen. You might get away with not having to replace a radiator cap at all throughout the life of your car if you get lucky. But there is also a chance that your radiator cap will stop doing its job for you at some point, which is why you need to know the signs that you need a new radiator cap.

What Are Some of the Signs That Show You Need a New Radiator Cap?

If you ever find yourself with a bad radiator cap in your car, you’re going to want to have it replaced right away. But before you can do that, you’ll need to spot some of the signs that will let you know that it’s time to have your bad radiator cap thrown out to make way for a new one. In certain situations, these signs will be painfully obvious to you, but in others, you might have to look a little harder to spot them. Here are some of the signs you should look for.

1. You Have Coolant Leaking From Your Car

The coolant that runs through your car’s cooling system is absolutely imperative to its overall function. If you don’t have enough coolant in your car, it’s often going to cause your engine to run hotter than it’s supposed to, which, as you might imagine, can cause all kinds of complications with it. With this in mind, you want to keep enough coolant in it and do whatever it takes to stop coolant from leaking out for any reason.


One reason why coolant might leak out of your car is because of a bad radiator cap. If you have a bad radiator cap, it’s not going to be able to release all of the excess pressure from your cooling system. That extra pressure will then often force coolant to escape from your system at the point that offers up the least resistance. This could result in coolant leaking from a bad radiator cap itself or from a hose, a water pump, or another area.


If you ever see coolant leaking from your car, you should take it off the road right away and have it repaired. In a perfect world, all you’ll need to do is replace a bad radiator cap to get it running like normal again. But you might also have other issues within your cooling system that lead to coolant leaking.

2. Your Car’s Engine Is Overheating

If you’re ever driving around in your car and the temperature gauge on your dashboard suddenly spikes, it should be a huge cause for concern. It often means that your coolant is way hotter than it should be, which can cause huge complications with your engine before long. You’re going to want to pull your car over as soon as possible to stop the temperature from getting even hotter than it already is.


A rising temperature gauge could indicate a serious issue with your cooling system as a whole. But it might also be an indication that you have a bad radiator cap. When the radiator cap isn’t allowed to maintain the pressure in your cooling system, it can impact your coolant’s ability to do its job, and it can lead to your engine overheating in no time at all. You’ll want to shut your car off right away and consider having it towed to a shop to prevent you from having to put your engine at risk again.

3. Your Car’s Radiator Hose Has Collapsed

You should always be very careful about opening your car’s hood if you suspect a problem with your radiator or another component within your cooling system. You could put yourself at risk if you open the hood and expose yourself to the high temperatures underneath the hood. But anytime you believe you might have an issue with your cooling system on your hands, you should let it cool off and then inspect it later to see what’s happening. And one of the things you should look at is your radiator hose.


If you have a bad radiator cap in your car, you’ll usually notice that your radiator hose will look like it has collapsed. This happens because of internal suction that builds up in your cooling system when your radiator cap isn’t performing up to its usual standards. This lack of pressure sometimes stops coolant from your car’s expansion tank from moving back into your cooling system and it results in your radiator hose collapsing. It’s an issue you’ll need to address with help from a mechanic ASAP.

4. Your Car’s Coolant Is Boiling

When you have a bad radiator cap in your car, the coolant in your cooling system is going to get very hot. It will eventually get to be so hot that it might even begin to boil. And that is obviously not going to be an ideal situation. When coolant boils, it’ll turn to steam, and before you know it, steam will start billowing out from under your car’s hood.


This is pretty much going to be a worst-case scenario for you when you’re dealing with a bad radiator cap. You’ll want to shut your car down and avoid going anywhere near it until you’re 100 percent convinced that it has cooled off. If you open your hood with steam still coming from your cooling system, it could burn you badly. It’ll also remove a lot of coolant from your car and make it unsafe to drive it without replacing the radiator cap and fixing any other issues with the coolant system.

How Should You Go About Replacing a Bad Radiator Cap?

If you have a bad radiator cap in your car and need to replace it, you might be able to get away with doing it on your own. It’s not all that difficult to remove your old radiator cap from your car and put a new one into its place. But if your radiator cap gets to the point where you’re seeing any of the signs we just mentioned, it wouldn’t be a bad idea to have a mechanic handle replacing it for you. They can inspect your car for signs of trouble in your cooling system before replacing your radiator cap and giving you the all-clear.


The last thing you want to do is make the mistake of diagnosing your car with a bad radiator cap when it has other issues within the cooling system. It could lead to more problems down the line and put you in a position where you do serious damage to the components within your cooling system or, worse, damage to your engine.

How Much Will a New Radiator Cap Cost You?

Despite the fact that the radiator cap in your car is such an important part, you’ll be happy to know that it’s not going to cost much to replace it. Most radiator caps cost less than $20 and can be replaced within just a few minutes, which makes radiator cap replacement one of the least expensive auto repair jobs around.


You might have to pay more to replace a bad radiator cap if you think you might have other issues with your cooling system, though. It’s good to know this going in, just in case your car needs to have more than just a bad radiator cap replaced. Whatever the case, you should prepare to make the necessary repairs to your cooling system. It’ll keep your engine running properly and prevent the need for major engine repairs in the future.

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