Updated at: 18-07-2022 - By: Lucas

A boiling coolant can be caused by a number of things, such as the coolant tank being depressurized, the thermostat being defective or failing, the coolant level dropping, or the cooling fan or temperature sensor failing. The most important thing to remember when dealing with boiling antifreeze is that you must immediately stop the vehicle.

If you keep driving like this, eventually your engine will break, requiring expensive and time-consuming repairs. However, removing the causes of the boiling of the coolant isn’t that tough, and even a beginner automobile owner may be able to handle it.

What are the causes of boiling coolant?

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To begin, let’s go over all the various reasons why the coolant is boiling.

1. Bad radiator

Keep the cooling system running smoothly using this car part’s primary duty. Nevertheless, mechanical damage or clogging on the inside or outside are possibilities. It’s best to examine the radiator first because it’s one of the most typical culprits.

2. Bad or failing thermostat

The thermostat’s primary function is to move coolant from the radiator to the so-called major coolant circuit before the engine reaches a predetermined operating temperature, often +85 °C (185 °F). As a result, the engine will quickly overheat, and the coolant will boil because there will be little time for it to cool.

3. Bad water pump

To avoid overheating, the amount of liquid that is closer to the engine heats up forcefully and boils as a result of its inability to circulate coolant.

4. Bad cooling fan

Its primary purpose is to cool down the components of the system that bear that name. In order to prevent the coolant from boiling, the cooling fan must be activated. During the summer months, this scenario becomes much more urgent.

5. The presence of air in the cooling system

The cooling system’s depressurization is the primary cause of its appearance. There are a number of reasons that contribute to this, including a drop in pressure, which means that the boiling point of the coolant is also reduced. Antifreeze inhibitors decay when exposed to air for a lengthy period of time, causing them to lose their ability to protect the engine. Finally, the level of coolant in the system decreases.

6. Low coolant level

As a result, the temperature rises above the critical level, causing the coolant to boil.

7. Bad temperature sensor

For example, the thermostat and/or cooling fan may not be operating properly because of a malfunctioning temperature sensor. The coolant is boiling since they didn’t switch on.

8. Poor coolant quality

Using a poor quality coolant in a vehicle will increase the likelihood that the coolant could boil, which can cause significant damage to the vehicle. A common example of this type of coolant is the fake stuff that frequently boils at temperatures as low as +100 degrees Celsius.

9. Foaming coolant

For a variety of causes, this can occur. Foam can be formed for a variety of reasons, such as using a subpar coolant, using the wrong kind of coolant for your vehicle, or damaging the cylinder head gasket, which allows air to enter the cooling system and react chemically with the coolant.

10. Depressurization of the tank cover

In either case, the safety relief valve may have failed or the gasket on the cover has failed. The coolant tank and radiator caps are both affected by this. It’s a result of this that the coolant’s boiling point is reduced because the cooling system pressure is equivalent to atmospheric.

It is vital to reevaluate the above causes in terms of their likelihood and frequency of failure in order to restore cooling system function and to keep coolant from boiling.

  • Expansion tank and its cap. This is especially true for cases when the coolant has boiled in the tank, and steam comes out from under it. Better to replace the entire valve cover.
  • Thermostat. This unit must be checked if the radiator is cold when the engine is running, and the antifreeze is boiling. Also, it makes sense to check the thermostat after replacing the coolant, if it immediately boils.
  • Cooling fan. It rarely fails, but it makes sense to check. As a rule, problems arise in dropped contacts or breakdown of the stator and/or rotor insulation windings.
  • Temperature sensor. This sensor is quite reliable, but it sometimes fails on older cars. The sensor controls the operation of the fan on the radiator
  • The water pump. Here it is similar to the previous point.
  • The radiator. It should be carefully inspected for damage and possible coolant leaks. If it leaks, then it is necessary to remove the radiator and inspect it. In most cases, it is recommended to replace it with a new one. You can just clean it if it is very clogged. It is better to remove it for external cleaning. As for the internal cleaning, this takes place together with the entire cooling system (without removing).
  • Check the level of coolant. It can leak out of the damaged system, and the remaining volume cannot withstand the heat load and will boil. If a poor quality liquid with a low boiling point is used, then it must be replaced completely. Otherwise, you can simply add coolant every time it drops.
  • Check if the coolant is suitable for the current car. If there was a mixing of two brands of coolant, then make sure that they are compatible with each other.
  • Check the function of the safety relief valve. You can check the operation of the valve on the cover using polyethylene.
  • Check the quality of the coolant. Quality coolant is always an excellent choice. Do not be stingy with this liquid of special importance for the cooling system. If you are uncertain of the quality, simply change it.
  • The consequences of adding bad or poor quality coolant are the boiling and destruction of the engine.

When does coolant boil?

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If you’re stuck in a traffic jam or on a lengthy road trip in the middle of summer, your car’s engine may overheat if you’re in low gear or running at fast speeds. On hot days, the air conditioning can make things even worse because of the added strain it puts on the cooling system’s main radiator.

The antifreeze level in the engine cooling system should be checked before embarking on a long journey.

TIP!Antifreeze containing more than 60% ethylene glycol by volume and less than 40% water is not recommended for usage.

Because to the presence of air in the cooling system, boiling coolant can be caused. Thermostat malfunctions, coolant leaks, and pump issues are all signs that it’s developing. In other words, if your car has even one of the issues stated above, it’s best to get it looked at as soon as possible before further damage is done.

What are the consequences of a boiling coolant?

The severity of the effects is determined by the engine’s temperature. So, this is all dependent on what kind of automobile you’re driving (engine power and body mass), what kind of engine you have, and how long it takes for the engine to cool down (the moment when it began to cool down). We can categorize the probable outcomes into three groups based on three different assumptions. Moderate and severe.

It’s possible that the engine pistons will melt if it’s overheated for a short time (up to 10 minutes). They can, however, alter their geometry. This isn’t a life-or-death situation for most people, unless there were prior issues with the geometry. It is sufficient to eliminate the reasons of coolant boiling if you discover it early and take the right procedures, which will be detailed below. An example of a less severe condition is shown here.

After the coolant has boiled for an average of 20 minutes, an overheating incident occurs. In this case, the severity is on the moderate side. As a result, the following breakdowns could occur:

  • curved cylinder head housing (relevant when the engine temperature reaches +120 degrees C (248 + F) and above);
  • cracks may appear on the cylinder head (both very small and cracks visible to the human eye);
  • melting or burning out of the cylinder head gasket;
  • failure (usually complete destruction) of the inter-ring partitions on the motor pistons;
  • the oil seals will begin to let the oil through, and it can either leak out or mix with the boiled antifreeze

There are several dangers that can occur if the coolant boils, and these are just a few.

However, if the driver ignores the boil and continues to drive, the so-called serious condition takes hold. It is possible for the motor to just erupt, burst, and fail in an extremely rare instance, however this rarely occurs. The following is a typical destruction sequence:

  • Melting and combustion of engine pistons.
  • During the above-mentioned process, the molten metal hits the cylinder walls, thereby hindering the piston movement. Ultimately, the piston will be destroyed.
  • Often, after the pistons fail, the car simply stalls and stops. However, if this does not happen, then problems with engine oil will begin.
  • Because the oil is also gaining a critical temperature, it loses its operational properties, which is why all the rubbing parts of the engine are put at risk.
  • Typically, small parts melt, and in liquid form, they will stick to the crankshaft, which makes it difficult to rotate.
  • After that, the valve sockets start to fly out. This leads to the fact that under the influence of at least one piston, the crankshaft simply breaks, or, in extreme cases, bends.
  • A broken crankshaft can easily break through one of the cylinder block walls, and this is equivalent to a complete engine failure, and, such a motor is unlikely to be restored.

A boiled coolant can have a devastating effect on both the car and its owner. In order to keep the cooling system in good working condition, it is vital to keep an eye on the antifreeze level regularly and, if necessary, execute any necessary repairs.

If the problem persists, then you need to fix it as quickly as possible.

What to do if the coolant is boiling?

First and foremost, do not be alarmed. It’s best to catch a partially damaged cooling system as soon as you notice it. This can be done both visually and with the aid of instruments by looking at the steam coming out of the engine compartment. The sooner you take action, the more probable it is that you will only have to pay for minor repairs.

  • Move the gear to neutral or idle to reduce engine RPM to idle.
  • Continue driving, and do not drop speed suddenly. The counter-air will be blown to the engine as much as possible to cool it.
  • While on the move, turn on the heat to the maximum at the highest possible temperature. Moreover, this must be done regardless of the season. This procedure is done to maximally remove heat from the radiator.
  • You need to roll as long as possible, until a complete stop. If it happens in the summer, then it is advisable to find a place to stop somewhere in the shade, without direct sunlight. After that, the engine must be turned off. In this case, the ignition must be left on to let the heater work for another 5 – 10 minutes. Then turn off the ignition too.
  • Open the hood to give maximum natural air access to the engine compartment. Without touching any engine parts with your hands, wait for a certain time. In summer about 40 – 50 minutes, in winter – about 20. Depends on the weather conditions and the time while the car was “boiling”.
  • Call a tow truck or a vehicle that tows the car to a workshop or a good mechanic with appropriate diagnostic equipment.
  • If there are no cars nearby, then after the mentioned time, making sure that there is no boiling and the liquid has “cooled”, carefully remove the cap of the coolant tank and add clean water. If you are not far away, you can use any non-carbonated drinks. Fill up to the mark.
  • Start the car, turn on the heat to maximum and continue to drive at low speeds. As soon as the coolant temperature reaches + 90 ° C (194 F), you need to stop and wait again for 40 minutes (or 20 if it’s winter). If you’re not far away, you’re in luck. Otherwise, you need to look for an option with a tow truck.
  • When you arrive in a workshop, tell the technicians about the problem, usually, they will easily find a breakdown (among those described above) and fix it.
  • Also, be sure to ask them to change the coolant, since the liquid that is currently in the system has already lost its performance properties.

Even a novice driver may complete the process outlined above because it is so straightforward. The most important thing is to keep an eye on the coolant as it heats up. A modest supply of coolant (ideally the same or compatible as the one currently in use) should be kept in the trunk, as well as engine oil. Despite its diminutive size, it can be a lifesaver when needed most.

What not to do when the coolant is boiling

  • Do not load the engine. Instead, you need to reduce the speed as much as possible to the idle value, usually around 1000 RPM.
  • Do not suddenly stop and turn off the engine, thinking that the engine will stop boiling, on the contrary, everything will only get worse.
  • Do not touch hot parts of the engine compartment!
  • While steam is coming out from under the cover of the tank or other unit and while the antifreeze is boiling in the system, it is absolutely impossible to open the cover of the tank! This can be done only after the time indicated above.
  • Do not pour cold water on the engine! You need to wait for the engine to cool down on its own.
  • After the engine has cooled down and you have added coolant, you cannot drive after reaching a temperature of more than +90 degrees.

Safety and economic savings are both yours if you follow these simple procedures.