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Summary
  • Coolant or antifreeze circulates through the cooling system and keeps your engine’s temperature stable. Coolant boils between 300 and 400 degrees Fahrenheit and when it does, it can indicate problems in your engine.
  • Common causes for boiling coolant include a faulty radiator cap, a blown head gasket, and incorrect or contaminated coolant. If your coolant boils, you can identify the resulting coolant leaks with a pressure test.
  • If your coolant is bubbling, turn off your engine to allow it to cool. Then, have your vehicle towed or drive carefully to an auto repair shop for inspection and repairs.
  • The best way to prevent your coolant from boiling and your engine from overheating is to take care of your ride’s cooling system.

The coolant or antifreeze keeps your engine’s temperature stable, but it needs to circulate through the cooling system to work. If anything disrupts the flow, your engine can overheat, leading to costly repairs and part replacements.

It’s normal for the coolant to get hot as it lowers the engine’s temperature, but is boiling coolant a cause of concern?

Reasons Why Your Coolant Is Boiling

Boiling coolant can indicate problems in your engine, so don’t disregard it. Here are some of the common reasons why coolant reaches its boiling point:

See also  Main Components of Your Cooling System

Faulty Radiator Cap

experienced mechanic checking radiator cap
When the cap is damaged or loose, air can enter the system and disrupt its operating temperature, which could cause the coolant to boil.

The radiator cap maintains the ideal pressure in the cooling system. When the cap is damaged or loose, air can enter the system and disrupt its operating temperature, which could cause the coolant to boil. A failed radiator cap can also cause the cooling system to vent, increasing the temperature even more.

Blown Head Gasket

Air can also enter the cooling system due to a blown head gasket. This can cause the coolant to boil and leak into the cylinder head, resulting in the engine overheating.

Bubbles in the coolant accompanied by white smoke from the exhaust might be a sign of head gasket problems.

Incorrect or Contaminated Coolant

The coolant can boil quickly if it’s the wrong kind for your vehicle. That could happen if you accidentally top it up with a variant different from what’s already in your engine.

The coolant and oil mixing can cause the coolant to boil. When your vehicle’s head gasket is blown or damaged, oil can leak into the openings and contaminate the coolant.

Bad Thermostat

When the coolant gets hot, the thermostat opens to let it flow through the radiator to cool. However, if the thermostat gets stuck closed, it could disrupt the cooling system and cause the coolant to boil.

You can read this article to learn more about the symptoms of a faulty thermostat.

What Temp Does Coolant Boil?

Coolant boils between 300 and 400 degrees Fahrenheit, while antifreeze boils between 225 and 300 degrees Fahrenheit. The coolant’s exact boiling point depends on its brand and type. Also, if you have too much water in your cooling system, expect the boiling point to drop even more.

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Do Bubbles In the Coolant Mean It’s Boiling?

No, a bubbling coolant isn’t always boiling. It might simply be a sign that the pressure in the cooling system is rising.

When air gets into the system, air pockets can form and cause blockages, which increase the system’s pressure. This can make the coolant bubble and increase the risk of the engine overheating.

What to Do When Your Coolant Is Bubbling

Turn off your engine and wait for it cool. Then, have your vehicle towed or carefully drive to an auto repair shop near you. Remember that bubbles in your coolant might be a sign that something is wrong with your cooling system, so don’t ignore them.

How to Fix a Boiling Coolant Issue

The fix depends on what’s causing the coolant to boil. For example, if it’s due to a bad radiator cap or a damaged head gasket, replacing it could resolve the problem.

If you’re not an expert on car cooling systems, it’s best to take your vehicle to an auto repair shop to address the issue. Mechanics can pinpoint what’s causing the coolant to boil and resolve it. They can also check the rest of the cooling system for potential issues that the boiling coolant might have caused.

Pressure Test

The coolant can leak when it boils, and one way to identify leaks in the coolant system is through a pressure test.

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You can buy or rent pressure testers from automotive part shops. Follow the tool’s instructions on how to conduct the test. You can also watch online videos to see how it’s done.

However, if you want to make sure you’re doing it correctly, you can ask for help from a professional. You can also leave the task to a mechanic.

How to Prevent the Coolant From Boiling

checking car coolant tank
Monitor the coolant’s level and condition, and check the coolant reservoir and tank regularly.

The best way to prevent your coolant from boiling and your engine from overheating is to take care of your ride’s cooling system. Monitor the coolant’s level and condition, and check the coolant reservoir and tank regularly. Take your ride to an auto repair shop regularly for its routine maintenance check-up.

Take your ride to an auto repair shop regularly for its routine maintenance check-up.

Anthony Harlin, ASE Certified Master Automobile Technician

Also, watch out for the symptoms of a boiling coolant, like bubbles and engine heat. Don’t let air enter the pressurized system. If you spot any of the signs, address them immediately to avoid costly repairs.

The US Department of Transportation reports that cooling system failure is the most common cause of highway mechanical breakdowns, so be observant. Don’t think twice about consulting a mechanic when you notice something unusual while you’re driving.

About The Authors
Written By Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at CarParts.com

Tony Harlin is a Master Gas and Diesel Diagnostic Technician with over 18 years of experience. He works full-time at a large independent automotive shop as a driveability and repair technician working on all types of vehicles with a focus on diesels. ASE certifications include A1-A9, L1 and L2, as well as X1.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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