Why Is My Coolant Boiling? (9 Reasons Why)

A complex system of pipes in your car’s cooling system circulates coolant through the engine, engine block, cylinder head, and head gasket.

But if there is a flaw, air can get into the hoses and lead to significant obstructions, which leads to boiling coolant. The engine overheating results from these flawed auto cooling systems.

So, let’s find out more about it!

Why Is My Coolant Boiling?

Your car’s coolant is boiling because of several different reasons. It could be due to a faulty water pump; of course, if your water pump is malfunctioning, it can no longer transfer coolant from your radiator to the engine block that, causes the coolant to boil. Other reasons could be a defective radiator cap, clogged radiator, a blown-out head gasket, broken thermostat, and pockets of air in your vehicle’s radiator.

Learn more about why your coolant is boiling. Here are nine reasons why. Keep reading to discover more!

1. Faulty Water Pump

To prevent overheating, a water pump transfers engine coolant from your vehicle’s radiator to the engine block. 

Although the water pumps in newer cars are more durable, driving a lot of miles damages the water pump.

Engine coolant leaks, steam coming from underneath the hood, overheating, and observable rust formation on the system are all indications that your water pump needs to be replaced. 

Further, you may also hear a whining noise whenever you accelerate.

2. Defective Radiator Cap

The radiator cap regulates the system’s overall coolant pressure. Three seals on this cap are susceptible to failure, which would stop the cooling system in its entirety, making your coolant boil.

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Collapsing radiator hoses, low coolant levels, leaking or spilling coolant antifreeze, and overheating are all signs of a damaged or defective radiator cap.

3. Clogged Radiator

How recently was the cooling system maintained and the coolant antifreeze drained? Engine coolant circulation is halted when debris obstructs the radiator’s water circulation system.

Smoke or steam flowing from the hood, boiling coolant, or an overheated engine are all immediate indicators of a faulty radiator.

Therefore, once you experience all this, take immediate action to avoid further damage.

4. Blown Out Head Gasket

You probably have a blown head gasket if you discover a leak in your cooling system close to your cylinder heads. 

In addition, air can enter the cooling system through a blown or faulty head gasket, which might end up causing your coolant to boil.

Further, foaming surrounding the coolant or expansion reservoir as well as air bubbles in your coolant, are further signs of a failed or damaged head gasket.

5. Pockets Of Air In The Radiator

Pockets Of Air In The Radiator

The possibility of air in your radiator is high. Air normally exists without a problem, but occasionally it remains caught. 

Of course, the cooling system cannot function correctly with trapped air. Your car becomes hotter as it runs longer and eventually overheats.

Therefore, the overheating experienced while driving normally, a broken heating system, and coolant leaks are all signs that there is air within the radiator.

6. Broken Thermostat

The circulation of coolant antifreeze from your vehicle’s engine to the radiator is monitored by the thermostat. 

That said, your engine may not receive the proper level of coolant to operate if the valve somehow doesn’t close or open as intended. 

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Both situations can cause the coolant in an automobile to boil, and both situations are harmful.

So, unexpected and irregular temperature changes, coolant leaks close to the thermostat, and temperature sensor readings are all indications of a malfunctioning thermostat.

7. Malfunctioning Temperature Sensor

The coolant temperature sensor keeps track of the engine’s temperature as well as the coolant antifreeze temperature. 

It also goes by the name CTS or ECT sensor, and it transmits temperature readings to the dashboard gauge.

Fuel efficiency and poor performance, a broken water pump, and sometimes even black smoke coming from the exhaust pipe are all symptoms of a defective sensor.

Therefore, be mindful of the symptoms so you would know when to take action.

8. Low Level Of Coolant

Your car’s coolant level may be too low if it starts to boil. Every two years or 30,000 miles, a car owner must flush and change the old coolant as part of good vehicle maintenance.

Additionally, low coolant levels result in poorer overall performance. You can encounter a failed heating system and decreased fuel economy. 

The thermometer can teeter on the edge of the danger zone, and you might smell something sweet.

9. Turbocharged Engine

The input boosts tension in your vehicle’s compressor, causing a turbocharged vehicle engine to operate at a high temperature. 

In addition, the car can suddenly fail if the temperature exceeds the normal threshold by a significant amount. 

So, if this occurs, a huge amount of smoke will be visible coming from the heated engine.

Your supercharger could still function, although not at peak efficiency if your car’s temperatures have become too high, yet it doesn’t break down. 

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Also, turbocharged engines can experience a dramatic rise in engine temperature on hot days or long journeys.


Overall, your coolant might be boiling due to several reasons and if you’re familiar with your car’s cooling system and engine, you might be able to identify the problem with a few short checks. 

However, before working on your engine, keep in mind that the automobile must be totally cool to avoid any injuries. 

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