Symptoms Of A Bad Radiator Cap & Replacement Cost

radiator cap

The radiator is an important part of a vehicle’s engine cooling system, which maintains the temperature of the internal combustion engine. The radiator cap is also a small but important component in the radiator system. The radiator cap plays a major role in the engine’s cooling system, even though it may seem to be a small component.

In this article, we will provide you with detailed information about radiator caps. Like, what is a radiator cap? How does a radiator cap work? What are the symptoms of a bad radiator cap, and what is the replacement cost?

What Is A Radiator Cap?

The radiator cap is a vital component of a vehicle’s cooling system, located on the neck above the radiator. This cap maintains optimal pressure within the radiator and ensures that the coolant does not boil at high temperatures and leak out. Additionally, the cap allows coolant to flow into the overflow reservoir and prevents air from entering the system, promoting efficient heat dissipation and engine performance, thereby avoiding engine overheating problems.

Symptoms Of A Bad Radiator Cap

Symptoms of a bad radiator cap include engine overheating, reservoir tank overflow, leaking coolant, fluctuating temperature gauges, collapsed hose pipes, or white deposits on the radiator neck.

Let us know in detail about the symptoms of radiator cap leakage so that you can save your engine from overheating in time..

1. Engine Overheating

smoke in radiator cap

If the radiator cap valve is not working properly, coolant will begin to leave the cooling system below this pressure value, due to which the engine will overheat. A low-pressure cooling system due to a bad radiator cap will cause the engine to overheat. So the engine starts overheating due to a bad radiator cap.

2. Overflowing Reservoir Tank

Overflowing Reservoir Tank

Excess fluid accumulates inside the reservoir tank. So that would be a sign of a bad radiator cap, which is usually a bad radiator top spring or something. A bad freezer seal will cause a quick release of coolant from the cooling system and cause the reservoir to overflow, if the coolant fluid in the reservoir tank is full. So this could also be a sign of a bad radiator cap. When this happens, you replace the radiator cap.

3. Coolant Leakage


If it’s the radiator cap is loose or loose. Then the radiator cap is unable to hold back the pressure of the hot coolant. A loose or faulty radiator cap can also result in coolant leakage from the radiator system due to overheating of the coolant. When a failure occurs on the gasket material of the radiator system and on this back seal.

Even then, there may be a coolant leak as well and when there is a leak of coolant. So the reason for this is that when the engine is hot, the coolant expands under high pressure and forms a gas. The valve on the radiator cap lifts up and opens at a certain point, due to which the hot coolant gas produced in the radiator system comes out and the coolant stops boiling.

4. White Deposit On Radiator Neck

White Deposit On Radiator Neck

There is some white deposit on the leak area around the neck of the radiator. If the radiator cap is not sealing properly, coolant will leak into the radiator neck. So if you see some white deposits in and around the radiator neck, this indicates a faulty radiator cap and this radiator cap needs to be replaced. Hence the fourth symptom: these substances accumulate on the components of the cooling system, especially on the neck.

5. Collapses or Shrink Hoses Pipe

Hoses Pipe Collapses

If your vehicle’s radiator cap is faulty. Then the hose pipes of your radiator system will start to shrink. because when the engine cools down after heating up, a vacuum is created in the coolant system and a faulty radiator cap can cause the vacuum to not be released properly. Because of this, one can see the rubber hose pipes shrinking or pressing due to the vacuum pull of the coolant.

6. Steam Coming From Engine Hood


As soon as the vehicle’s engine has run for some time after starting it. Then the temperature of the engine starts increasing gradually, due to which the coolant fluid inside the engine starts heating up, and after some time the coolant fluid comes to a boiling point.

And starts making steam. If your vehicle’s radiator cap is faulty, then you may see steamy smoke coming out from around the engine of your vehicle. Often, this vapor like smoke is seen coming out very quickly due to the cap of the radiator.

How Does A Radiator Cap Work?

A radiator cap has mainly two functions.

1. Use For Coolant Pressure

So when the cooling system is pressurized, there is an increase in the boiling point and due to the pressure, the coolant flows for a long time without boiling. So when the cooling system is pressurized, your vehicle’s engine will get good cooling, so that pressure can be created when the coolant is heated by the radiator cap. When only the cooling pressure is high enough, this pressure will lift the valve and then the coolant would start leaking into the reservoir. So the pressure valve operates it. Therefore, the first function of a radiator cap is to increase the pressure of the cooling system.

2. Vacuum In Coolant System

Whenever the engine of a vehicle cools down after heating up, a vacuum is created in the coolant system. The radiator cap serves to prevent excess vacuum from building up in the coolant system and forcing coolant from the reservoir back into the cooling system.

This prevents shrinkage in the components of the cooling system. which is provided by a vacuum valve on the radiator that allows a vacuum to be drawn. Due to this, the hose pipe of the radiator is saved from shrinking and helps the flow of coolant to flow perfectly.

Radiator Cap Replacement Cost

Radiator cap replacement costs on average can range from $5 to $30 for typical cars. You may not need a mechanic to replace it. Because replacing the radiator cap is a very easy task in many cars, you can replace the radiator cap yourself in a matter of seconds. However, do take some precautions while replacing the radiator cap.

Precautions –

  • Never open the radiator cap on a hot engine, even by mistake. Doing so will prove harmful for you.
  • You will need to wait for the engine to cool before replacing the radiator cap.
  • Never point your face directly at the radiator when opening the radiator cap, as the high pressure of the coolant could cause coolant fluid to splash into your face and eyes.


Q. Is it ok to drive without a radiator cap?

No, it is not safe to drive a vehicle without a radiator cap. Without the radiator cap, the coolant boils out. Due to which the coolant of your vehicle’s engine can end and running the engine for a long time without coolant can cause the engine to overheat. And due to this, the engine head gasket may get damaged. A permanent shutdown may occur due to engine damage.

Q. How do I know my radiator cap needs replacing?

You may experience the following symptoms when a radiator cap is failing or defective:

  • Leaking coolant
  • Over temperature display of the temperature gauge
  • Collapsed radiator hoses pipe
  • Overflow reservoir tank
  • White buildup around the radiator cap

Q. How often should the radiator cap be changed?

There is no set time to replace a radiator cap. Generally, the radiator cap of a vehicle can last for 3–5 years. The radiator cap can usually be replaced when it shows signs of failure.

Q. Why is my car overheating but it has coolant?

Having such a problem could mean that the coolant system of your vehicle’s engine is getting faulty. That is, the coolant is not flowing in sufficient quantity in the engine’s cooling system. There can be many reasons for this. Such as :- water pump failure or serpentine belt breakage, radiator blockage and radiator hoses pipe burst.

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