Why Is My Antifreeze Boiling?

The car antifreeze systems depend on a close-up network of pipes to circulate antifreeze or coolant around the car’s engine. These pipes are placed in a conserved ring, allowing a consistent and seamless passage of the liquid to reach components such as the cylinder heads, engine block, and head gasket – ensuring the engine is running at the proper temperature.

When your car antifreeze begins to boil, it indicates an internal problem. It could be any of the following issues: the engine fans are not working, trapped air, clogged radiator, imbalanced water ratio, bad radiator cap, or blown gasket. These and more are why your car antifreeze is boiling or, per se, overheating.

When airflow leaks into this enclosed system, clogs and bubbling might occur, causing an overheat in the engine. It could be that you used the wrong antifreeze fluid or a low level of antifreeze or coolant. There are various probable explanations for air trapped in a car cooling system, which we will go over in this guide on why your car antifreeze or coolant boils. Let us narrow down the problems and find solutions.

What Can Make My Coolant Boil Without Causing Overheats?

The primary cause for this is a faulty radiator cap. At this point, the pressure needed within the system is no longer held tight by it. If replaced, there will be water in the system, leading to overheating. The coolant travels into the reservoir tank when you start your vehicle. However, if the cap is bad and not enough pressure is applied, then the coolant will not be released slowly, leading your reservoir to boil.

What Can Make My Coolant Boil Without Causing Overheats

Why Your Antifreeze Boils?

When your car engine overheats, coolants or antifreeze are incorrectly circulating through the engine. If the coolant level is low due to evaporation or leaks over time, there could be an engine boil. The best way to avoid these is to check the system for leaks and blockages in the hoses or pipes.

Why Your Antifreeze Boils

Here are the reasons why your antifreeze boils:

Very Hot Engine

Your coolant or antifreeze can boil due to it being too hot. Do not be afraid- this is a common issue, and there is no cause for alarm. Know that all engines become significantly hot and require cooling down at some point to keep working flawlessly. The boiling of your engine is a sign that you should always keep a 50-50 water to coolant ratio in your radiator. If you are not confident handling hot temperatures, getting help as soon as possible ensures your vehicle will keep working properly.

Stagnant Coolant

When the coolant becomes stagnant or static, it begins to boil as there is no movement or passage to the other components in the engine. It will cause the coolant to gain more temperature in that same spot. However, you either have the wrong coolant-water mix ratio, sluggish flow of coolant, static antifreeze, or a torn head gasket.

Defective Radiator Cap

A cooling system under pressure is required to keep your radiator functioning properly and keep the antifreeze from overheating or boiling. A malfunctioning radiator cap can cause boiling antifreeze. Aside from that, below are the signs of a defective radiator cap: leakage of antifreeze fluid, boiling or overheating antifreeze fluid, or uneven cooling system pressure. Therefore, when you notice any of the signs stated above, know that your radiator cap has a problem that led to the boiling issue. Radiator caps do not cost much; it is crucial to keep the cooling system sealed and ensure it is always pressurized.

Defective Radiator Fan

As a car is nothing without its tire, so is a radiator without its fan, and the fan is the primary component of a radiator. There are various car models; your car might have a double or single radiator fan. Whichever one your car has, the most important job of the fan is to keep the coolant cool at all times. If the fan becomes faulty somehow, it will cause the coolant to boil.

Faulty or Bad Thermostat

Most car owners do not know the crucial roles a thermostat plays in keeping their engine under the right temperature. Its primary function is to regulate fluid and monitor the temperature of the antifreeze, and it opens up the inflow of fluid and decreases the engine temperature. However, when the thermostat malfunctions and fails to open properly, it may cause your antifreeze reservoir to boil.

What You Should Do When Your Antifreeze Is Boiling?

Most car owners fail to understand the steps they should take when their car antifreeze boils or overheats. In a situation like this, the first thing you should do is park your car in a safe place. At this point, you are yet to ascertain the cause of the boiling. Secondly, check your engine temperature. Do this by looking at the temperature gauge at the driver-side dashboard. If you see your engine’s temperature gauge is at the red spot, turn off your car immediately.

What You Should Do When Your Antifreeze Is Boiling

If the antifreeze is boiling, but your vehicle is not overheating, you have to open up the antifreeze reservoir lid. Take note not to open the radiator but the antifreeze reservoir, and you should not open the radiator unless the vehicle has cooled down. It will help avoid any heat and pressure build-up in the coolant system. Opening the reservoir gives the system air pocket room to belch out slowly from the system.

Fixing the Boiling Issue

There is always a way to fix a car problem- here; we will focus on the antifreeze boiling. Firstly, you have to detect why it is boiling. Once you have seen the faulty part, the next thing is to replace the part to solve the problem. Try to follow other steps to be able to diagnose a defective part.

A head gasket may cost as low or as much as $500. The repair cost propels many car owners to sell off their cars. However, it is hard for a head gasket to develop a fault. Do not be too quick to conclude and sell off your ride.

Sometimes a misdiagnose can occur. Before giving yourself a problem to worry about, get back to the root of the problem or ask for an expert’s opinion. If someone suggests a blown head gasket, look out for bad head gasket symptoms. You can also check if your car antifreeze boils inside the reservoir. Suppose the smoke from your exhaust is white or your vehicle ran roughly when you drove it the last time.

Remove your engine oil fill lid, flip the lid upside down, and check the color of the oil in the cover to see if it is whitish. If you have non-whitish oil, your head gasket is not blown, and you should look out for another cause of the problem.

How to Prevent the Antifreeze from Boiling

As the saying goes, “prevention is better than cure.” It is best to save your car antifreeze from boiling by maintaining your car. Car maintenance is essential for the proper function of your car. So, keeping up-to-date maintenance of your vehicle will help eradicate minor problems early to avoid bigger problems.

Unscrew the lid of the antifreeze or coolant reservoir and start your vehicle. After it has finished running, the fan should turn on. Check that your air conditioning system is at an average hot temperature as possible. Then, make sure that your air conditioner’s fan is completely charged. Check that the antifreeze reservoir is full of liquid. Lastly, stuck air that has been released may be restored when the antifreeze level is reduced.

Boiling Point for Antifreeze

You can determine the level at which antifreeze or coolant boils by the quality of products and the tension retained within the system. Preston antifreeze has a boiling temperature of 129°C and freezes at -37°C under typical operating conditions. Suppose the pressure within the system is affected by leakage or any broken part, such as the head gasket, it can lead to more issues for your vehicle. The point at which the coolant boils will fall while the pressure within the system reduces. As a result, if your automobile has a defect or a leakage, it might cause overheating, and the antifreeze/coolant in the system can boil.


In conclusion, your car’s antifreeze acts as a heat absorber, minimizing the total temperature of your engine as your car runs. If the antifreeze liquid is boiling, it could be that they are not performing properly due to diverse issues. It includes a defective radiator cap, blown head gasket, thermostat, radiator, and a broken fan. Also, a dirty coolant can lead to build-ups; hence, the liquid cannot flow freely through the reservoir.

We hope this article answered your question on why my antifreeze is boiling. You may now choose to fix it yourself or pay an expert since we have mentioned the most basic fixes. Noting all the above problems and their solutions will help you know where to start in solving your such issues.

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