Symptoms of A Bad Radiator Cap: Common facts to know as a Car Owner!

Symptoms of A Bad Radiator Cap

Cooling System is one of the Most Important Sections of an Automotive Engine. There are two types of Engine cooling systems we see often. Air Cooled system and water-cooled system or liquid-cooled. Almost every motorcycle has an air-cooled Engine nowadays, some of the motorbikes have liquid-cooled engines too. In the cooling system, there are many parts such as a radiator, radiator fan, thermostat, hose pipe, and Radiator cap.

Our today’s topic is Symptoms of bad radiator cap as well as a few important tips and tricks regarding this issue. After finishing this article, you’ll get to know a few common facts that you must know as a driver or a car owner.

When you start the engine of your vehicle, the coolant temperature increases too fast. Sometimes, the boil point temperature becomes 118 degrees at maximum. As the pressure and the temperature increases parallelly, the coolant pressure can be increased parallelly at the same time and the radiator cap can absorb the pressure of 8 PSI to 16 PSI.

However, here are a few symptoms of a bad radiator cap. With these, you can easily determine you should fix it or replace it as soon as possible.

#01.Coolant leaking

If the radiator cap is stuck, the proper amount of coolant cannot be released appropriately and this causes coolant temperature and coolant pressure increasing. This drives to consequent leaking of the coolant through the radiator pressure cap. Leaked coolant stays in between the radiator upper tank and the radiator upper body. Sometimes, you may only notice the liquid color. This is because of the liquid vapors. If you see this type of symptom, you should replace it immediately.

Also must be looked at the hose clump of radiators some times lose or overtighten hose clump make coolant leak.

#02. Radiator hose collapsed

Bad Radiator Cap can collapse the radiator hose due to improper vacuum released through the radiator cap while coolant temperature minimizes. If you notice such types of symptoms, you must inspect the radiator cap.

If you find out any problem or any kind of damage to the seals or the springs of the radiator cap, you should replace it immediately.

#03.The air in the cooling system

Another important symptom is this one, air in the cooling system. If your radiator cap becomes bad, it gives the air access to the radiator cooling system. As a result excess air goes inside it. If your car radiator cap seal is Hard or damaged, it can cause excess air deposits inside the radiator.

The air in the cooling system can make some extra unnecessary pressure and it can increase the temperature of your car coolant. Sometimes, it damages the hose pipe. So, it’s essential that you keep the radiator cap proper tighten and you use a suitable one for your vehicle.

#04.Antifreeze backing up in overflow tank

Sometimes, you may notice that the coolant backing up into the reservoir. This can happen if the radiator cap is not working and operating well. If your radiator cap does not perform well, the coolant won’t return when it’s required. This one is a symptom of a bad radiator cap.

Related Article: Oil in Coolant Reservoir: Common Symptoms, Reasons as well as Solutions

If you notice such types of symptoms, you should check the radiator cap immediately. If you see the damaged sign of the radiator cap, it should be replaced. Sometimes, the water pump can cause the same problem. So, it’s better you have your vehicle checked by an experienced mechanic.

#05. Engine overheated

An overheated engine is a very significant issue. There are so many reasons those can make your car engine overheated. Such as fault of radiator Fans, Thermostat, Coolant, Fan Motor or Viscus fan or any other electric line.

The radiator cap is one of those parts which we ignore often. But it can make your engine overheated too. Any fault of the radiator cap can make a lot of problems including engine overheat. So, you have to find out what the actual problem is. If you can’t do it, go to your reliable garage or mechanic.

Symptoms of A Bad Radiator Cap

How to test the radiator cap?

You Can Easily Test the radiator cap with some physical inspections. Just open the radiator cap and inspect carefully. If you observe any kind of damage to seals or springs, it should be replaced. Another way is radiator cap checkup by using a radiator cap pressure tester. If you have this in your garage, you can do it yourself:

Required equipment and material:

  1. Radiator pressure tester
  2. Coolant
  3. Tray
  4. Some cloth
  5. Work Light ( Optional )
  6. Tool Box
  7. Hand Gloves

Step 1: Make sure the vehicle coolant temperature is normal. You should wait until the temperature is normal. Don’t attempt to remove the radiator cap while the engine is started or in high temp condition.

Step 2: Once the Engine is cooled down enough and you can touch easily the radiator hose and other parts of the radiator. Just remove the radiator cap from the radiator.

Step 3: Attach the Radiator Cap with the Radiator cap pressure tester adaptor.

Step 4: Now, pump the pressure handle until it reaches according to the level written in the radiator cap. If you notice massive lose pressure then your radiator cap is not okay. But a little loss is normal and considerable. What you need to check is, the radiator cap must have to able to hold the maximum pressure for a minimum of 5 minutes.

Step 5: Set back the old one if it’s okay or buys a new one from the market by showing your brand, maker, year, and model.

  Source : (

How to test a radiator cap AND not get false results! YouTube Video

The FAQ (Frequently Asked Questions)

Q: How do I know when my radiator is bad?

A: Check coolant issues and check if your engine gets overheated too quickly or not. If it does, then maybe you have a bad radiator. Besides, compare your car with our symptoms described above.

Q: Can a bad radiator cap cause too much pressure?

A: No, it helps to keep your cooling system pressurized carefully. But if your radiator is fallen down or bad, it can’t give the sufficient pressure your vehicle need. So, there’s no chance of too much pressure.

Q: Can a bad radiator cap cause bubble?

A: No, a faulty thermostat can cause bubbling and churning. There’s no connection between bubbling and bad radiator cap or head gasket.

Q: What happens if the radiator cap does not hold pressure?

A: When the radiator cap does not hold pressure a lot of problems happen with the engine and vehicle. Sometimes there is some coolant issue. Car overheats frequently. So it’s pretty essential to keep the radiator cap pressure according to its needs.

Q: How do you know if your thermostat is bad in your car?

A: By troubleshooting with a temperature gauge. To more about troubleshooting and how to do it, click here!


So, these are the basic and common symptoms of a bad radiator cap. If you find out any of these, have your car checked as soon as possible. Then, if the radiator cap requires changing, change it. If you find any other problems don’t forget to solve them too.

To read other articles like this one, visit our website. If you have any questions and query feel free to leave a comment here or contact us directly!

Recent Posts