What Does It Mean if Car Coolant is Boiling/ Bubbling?

Coolant/antifreeze is pumped around an engine through a sealed system of pipes. These hoses are placed in a sealed loop, which permits a smooth and consistent flow of radiator fluid to reach components such as cylinder heads, the head gasket, and the engine block – maintaining the engine’s optimal temperature.

When air is permitted to enter a sealed system, obstructions and bubbling might occur, leading to an overheated engine. There are a variety of possible explanations for tiny bubbles in the cooling system, and we will discuss what it means when coolant is boiling or bubbling.

Why Is My Car’s Coolant Bubbling/Boiling?

Most automobiles’ cooling systems are pressurized and rely on a closed circuit of leak-free tubes to circulate an all-around coolant engine. When air enters a system, air pockets can develop and produce obstructions, resulting in bubbling and overheating.

The presence of bubbling implies an increase in air pressure in the cooling system, which indicates a blockage in the flow of liquid. The air pressure in the cylinder heads is transmitted to the cooling system due to a blown head gasket, which is one of the most frequent reasons. This air loss creates a bubbling/boiling effect in the coolant reservoir, sometimes misinterpreted as boiling.

Besides a blown head gasket, there are also several potential reasons for air in the cooling system, which we will discuss later.

How Does Air Get In The Cooling System, And How Can I Fix It?

There are some reasons why air can get in your car’s cooling system and range from minor to major mechanical issues that require immediate rectification. Below are some of the causes and possible ways to fix this problem.

1.    Blown Head Gasket

When a head gasket fails, pressurized air from cylinders can quickly enter the cooling system, causing the reservoir to bubble and coolant/antifreeze to leak into the cylinder head.

Some of the symptoms of a blown head gasket include:

  • Overheating engine
  • White smoke coming from the exhaust
  • Coolant leaks
  • Loss of power while driving
  • Bubbles in the coolant

2. Thermostat Is Stuck Closed

The thermostat is responsible for regulating the flow of coolant through the engine.

If the thermostat becomes stuck in the closed position, then the coolant will not be able to flow through the engine and remove the heat. This can cause the coolant to boil and cause the engine to overheat.

3. Clogged Radiator

One of the main reasons why your car coolant is boiling is because your radiator might be clogged. If there’s insufficient airflow, the engine will overheat, and the coolant will start to boil.

Many things can clog a radiator, but the most common culprit is scale. Scale is a build-up of mineral deposits that can occur over time, and it can gradually restrict the flow of coolant through the radiator.

This can cause the engine to run hotter than normal, eventually overheating. To prevent scale from forming in the first place, it’s essential to use a good quality antifreeze/coolant that contains inhibitors.

These inhibitors help to prevent scale from forming and also help to keep the existing scale from getting worse. If you already have a build-up of scale in your radiator, there are specialty cleaners that can help to remove it. However, in severe cases, it may be necessary to have the radiator professionally cleaned or replaced.

4. Defective or Faulty Radiator Cap

The radiator cap is a crucial piece of your cooling system. Its main purpose is to maintain pressure in the system, which helps to raise the boiling point of the coolant.

A defective radiator cap can cause your engine to overheat.

The pressure in the cooling system will build up and cause the coolant to boil. This can damage your engine and cause it to fail. To avoid this, check your radiator cap regularly and replace it if it is damaged or faulty.

Symptoms of a faulty radiator cap

  • Bubbles forming around the cap seal
  • Overheating

5. Coolant Level Is Low

If the coolant level in your radiator is low, it will not be able to remove heat from the engine effectively. This can lead to the coolant boiling and causing the engine to overheat. Check the coolant level in your radiator regularly and top it off as needed.

Low amounts of coolant also degrade overall performance. You may encounter decreased fuel economy and heating system failure. The temperature gauge may approach the red zone, and you may detect a sweet smell.

6. Bad Cooling Fan

A car cooling fan is a device that helps circulate cool air around a car’s engine. It is usually located in front of the radiator and is used to help keep the engine cool.

The cooling fan helps to prevent the engine from overheating by circulating cool air around the engine. If the fan isn’t working properly, it won’t be able to do its job, and the coolant will start to boil.

Two types of cooling fans can be used in a car: an electric fan or a mechanical fan. An electric fan is powered by the car’s battery and controlled by a switch on the dashboard. A mechanical fan is powered by the engine and controlled by a lever on the side of the engine.

7. Bad Water Pump

Water pumps typically have a lifespan of 100000 miles or more, which is crucial in controlling engine temperature due to their essential function. The component continually injects coolant into an automobile’s engine to avoid overheating.

What would occur if the water pump failed? It will cause the engine temperature to rise to a hazardous level. This is often signaled on the dashboard by an engine overheating or check engine light. At this point, the coolant becomes heated, boils, emit white smoke, and raises the temperature of the entire vehicle.

8. Faulty Thermostat

The first sign of a defective thermostat is engine overheating. The car’s temperature gauge may indicate an excessively high temperature, allowing for easy detection.

Because the valves are trapped in the closed position, this situation may have occurred. Therefore, the coolant will be incapable of flowing and boiling.

A thermostat’s job is to open and shut periodically to regulate the flow of coolant to and from the radiator. When the thermostat fails to function correctly, it won’t open at the precise moment, causing the coolant system to overheat.

Why Is My Coolant Boiling Fixes

Fix Air Pocket in Car

The issue may be readily remedied by correctly filling it with coolant. At the same time as the coolant is being replaced, the utilized air is retained inside the tank, generating air bubbles and increasing the temperature of the coolant.

To ensure there isn’t any air in the reservoir, turn on the engine with the radiator cap off. It will aid in depressurizing your tank.

Repair Radiator and Radiator Cap

The radiator cap may be inspected using a pressure gauge if the pressure decreases throughout the test, attempt to wipe the cap and retest.

If it continues to produce the same consequences, you must immediately replace the radiator cap. Generally, the radiator cap is relatively affordable and can be purchased at any auto repair shop; nevertheless, you must ensure that it has the correct pressure rating.

With regular maintenance, a radiator may last between eight and ten years. When you observe bubbles or boiling coolant, you must examine or replace your car’s radiator. A blocked radiator can cause engine harm by causing the coolant to overheat and finally boil.

To remedy this, you can clean and flush the outside fins according to the manufacturer’s maintenance plan. When the radiator is far beyond repair, replace this component. Sadly, radiators are both an expensive and labor-intensive piece of equipment and procedure. The cost to replace a radiator ranges from $182 to $921.

Replace Bad Thermostat

When the thermostat gets blocked, the coolant in the engine cannot circulate to the radiator. In this circumstance, the thermostat must be replaced. For most do-it-yourselfers, replacing or repairing a faulty thermostat is a straightforward process, while others do not know where to begin.

If you have auto maintenance skills, you can change the thermostat on your own; if not, you may take your vehicle to a reputable technician. The cost to repair a thermostat ranges from $70 to $450, dependent on your vehicle’s type and labor. A thermostat costs between $20 and $50, and manufacturing labor costs from $50 and $400 per hour.


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