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coolant blows out of reservoir

7 Reasons Why Coolant Blows Out Of Reservoir & Fix

The coolant blows out of reservoir sometimes. It means that you are having problems with the engine cooling system. Do not ignore it because your engine will get overheated after that, causing severe damage. 

There are multiple reasons for this issue. Most of them come from broken parts in the cooling system. If you use the coolant improperly, you may encounter the same case.

So what should you do now? We will explain the reasons for the coolant overflowing from reservoir first. Then, join us to find out the right solution for your situation.  

coolant blows out of reservoir

7 Reasons Why Coolant Blows Out Of Reservoir

The coolant blows out of the reservoir because of the damaged water pump, broken thermostat, and faulty head gasket. The amount and quality of coolant contribute to the problem, too. 

What does it mean when the coolant blows out? It’s a condition when the heat transfer fluid seeps into the car’s system from the reservoir.

The overheated engine is the first symptom to check for. And once it becomes too hot, the whole system will malfunction. Please remember that the engine powers your car. So any problems with it can lead to significant damage. Hence, many drivers consider swapping the engine to improve their car performance. 

This issue has several potential reasons, but heat-related problems play a significant role. It’s because the temperature fluctuation causes the coolant to heat up quickly and expand in volume abnormally.

Damaged Water Pump

Damaged Water Pump

The water pump is in charge of taking water around the radiator and the internal combustion engine. It also helps maintain the optimal water temperature. If the water becomes too hot, the water pump will cool it down.

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As a result, when broken, the water pump may overheat the internal combustion engine, damaging your vehicle. You will notice coolant bubbling out of reservoir, too. 

The lifespan of a water pump is generally from 60,000 to 90,000 miles. Once it reaches the limit, you should replace the pump and its timing belt. 

Other signs of a bad water pump include abnormal noise, a hot engine, rust, and antifreeze leaking.

Broken Thermostat

The thermostat regulates the engine’s temperature by managing the coolant flow across the engine. However, it gets stuck and fails sometimes. Then, the coolant can’t circulate properly and cause your engine to overheat. 

The heated engine will create pressure in the cooling system, making the coolant blow out of the reservoir or other parts of the system. 

Broken Head Gasket

Broken Head Gasket

The head gasket seals the coolant passages and combustion chambers. It rests between the cylinder head and the engine block. 

If the head gasket can’t perform its task properly, the coolant will leak into the engine passages or combustion chambers. Then, the engine will lose its power and become overheated. 

The combustion gas escapes through the damaged head gasket. It will create a pressure that pulls the coolant out of the cooling system. 

Bad Coolant

Before choosing and applying coolant for your automobile, you must always check the coolant’s quality carefully. This liquid may result in overflow and cause systemic issues.

The cooling water should be stable and retain heat during travel. When mixed poorly, it can’t dissipate the heat properly. That’s why bad coolants heat up fast and have a low boiling point. 

All the issues above will make the liquid reach the expansion threshold. As a consequence, the coolant will leak while the system isn’t too hot. 

Inappropriate Amount Of Coolant

If you add too much coolant, the pipeline volume will increase. In this case, even a small temperature can make it expand considerably, pushing the coolant out of the reservoir. 

On the other hand, adding too little coolant also causes a blowout. The cooling system will malfunction when it lacks coolant, leading to liquid spills. 

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Unactivated Cooling Fan

Unactivated Cooling Fan

The radiator will fail and overheat when the wires become rusty. If the cooling fan can’t offer sufficient air circulation for the radiator, your engine will overheat. 

The malfunctioning cooling fan may cause a hot engine, a blown-out fuse, broken wires, and a bad relay. The coolant will also blow out because of the overheated engine. 

Blocked Radiator

If your car doesn’t have any signs of the above issues, it can be the blocked radiator to blame when the coolant blows out. 

The radiator plays a vital role in the cooling system. When the coolant travels through it, heat will form. And after passing the radiator, the coolant will get cooler. 

The radiator may become clogged because of the accumulated sediment and rust particles in the tubes. The blockage will cause a coolant backup. There may be no pressure in the radiator , too

If you don’t notice and eliminate the blockage, it will get bigger day by day. The excess coolant will spill out of the reservoir as a result. 

Coolant Blows Out Of Reservoir fix

How To Fix It When The Coolant Blows Out Of Reservoir?

After finding the answer to “Why is coolant reservoir overflowing?”, we can tell that there are various reasons to expect. To determine the exact cause, you must stop your car first to avoid further damage.

The engine should cool down before your checkup. Do not remove the radiator cap or reservoir cap while the engine is still hot. Otherwise, the coolant will spray out and cause serious burns.

Then, check all the potential causes of steam coming out of coolant reservoir, such as:

  • Leaks in the engine, hoses, water pump, and other parts of the cooling system
  • Coolant level (add more if it’s too low)
  • The working condition of the thermostat, water pump, radiator, and head gasket

Most of the time, you need to contact a qualified mechanic to fix the issue. The broken part often requires a replacement.  

Choosing the right coolant is also essential for maintaining your car engine’s performance and durability. It won’t blow out of the reservoir easily. But which coolant is the best for your engine?

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You can check the owner’s manual for the recommended option for your specific make and model of car. Then, choose a reputable brand to get high-quality products. 

How To Prevent My Car Coolant From Blowing Out Of The Reservoir?

It’s easy. You just need to maintain the cooling system properly to prevent the coolant from blowing out of the reservoir. Here are some steps to take:

  • Establish regular maintenance and follow it strictly. The tasks include coolant replacement, infections, and repairs. 
  • Use high-quality coolant and ensure it’s always at the recommended level. 
  • Check for the signs of leaks in the system regularly. 
  • Replace the pressure cap when needed. 
  • Clean the radiator, so it allows the coolant to flow properly. 

How Much Does It Cost To Fix The Coolant Blowing Out Of The Reservoir?

The repair cost differs depending on the cause. The service you choose also affects the overall fee. For example:

  • Damaged water pump: $500 or more
  • Leakage issue: $50 to $500
  • Thermal sensor: $150 or more

What Is The Boiling Point Of The Engine Coolant?

The quality of the product and the pressure kept inside the cooling system influence the boiling temperature of the coolant. Under standard operating pressure, the liquid often has a boiling point of 129°C. Its freezing point is -37°C.

Nevertheless, a leak or damaged part, such as a cracked head gasket, affects the pressure inside the coolant. Then, the boiling point will fall as the pressure inside the system drops.

As a result, when your car has a leak or error, it may overheat. In this scenario, the coolant in the system will boil and blow out of the reservoir. 


The coolant blows out of reservoir because of the faulty head gasket, water pump, or thermostat. If you use poor-quality coolant or the coolant level is too low, it will leak out, too. 

The solution for your case depends on the cause. Remember to check the cooling system carefully to diagnose the issue. 

Hopefully, you won’t have any problems with the coolant. If you experience other cases, do not hesitate to contact us for help. 

Thank you for reading! 


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