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Cars & Other Vehicles
Cars
Car Maintenance and Repair
Vehicle Fuels and Fluids
How to Check Coolant Download Article Co-authored by Jason Shackelford
Last Updated: February 24, 2025 References
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Checking the Radiator
|
Looking at the Overflow Tank
|
Making Sure Your Coolant is Effective
|
Video
|
Expert Interview
|
Q&A
|
Tips
|
Warnings
|Show more|Show less X
This article was co-authored by Jason Shackelford. Jason Shackelford is the Owner of Stingray Auto Repair, a family owned and operated auto repair shop with locations in Seattle and Redmond, Washington. He has over 24 years of experience in auto repair and services, and every single technician on Jason’s team has more than 10 years of experience. There are 9 references cited in this article, which can be found at the bottom of the page. This article has been viewed 50,094 times.
The cooling system of a car is designed to remove heat from the engine. In order for the cooling system to do this, the right amount of quality coolant, also called antifreeze and radiator fluid, should be added to the radiator. It's important to check that your car has this coolant to ensure that the engine is working effectively. To do this, you need to assess the levels in the radiator and the overflow tank and check the effectiveness of the coolant in your system.
Steps
Method 1 Method 1 of 3:
Checking the Radiator
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1 Park the car on a level surface. If the car is not level, for instance if it is parked on a hill, you cannot get a true reading of your coolant level. In fact, if you open up your radiator cap while parked on a hill it could cause coolant to pour out.[1]XResearch source
2 Make sure the engine is cool. It is very important for your safety that the engine is cool before you open up the cap on the radiator. The radiator is under pressure and displaces a lot of heat, so it can scald you if the engine is not cool before you open it.[2]XResearch source
However, if it's an emergency, such as your car is overheating, you can check your coolant by covering the radiator cap with a thick rag to deflect heat and steam.
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3 Open the radiator cap. The radiator is at the front of the engine and has a cap on the top of it. In order to remove the cap you will need to press down on it and twist at the same time.[3]X Expert Source Jason ShackelfordAuto TechnicianExpert Interview In many cases, it will take 2 hands to put enough downward and twisting pressure to get it off because there is a vacuum created inside the radiator.[4]XResearch source
To keep coolant off your hands, you can cover the cap with a rag as you take it off or wear a pair of gloves.
4 Ensure the coolant reaches the top of the radiator. When you take off the cap you should be able to see the coolant right at the top.[5]X Expert Source Jason ShackelfordAuto TechnicianExpert Interview If the coolant is lower or you can't see it, your coolant level is too low.[6]XResearch source
On some radiators there will be a "full" mark near the top. This is where the coolant level should be.
Advertisement Method 2 Method 2 of 3:
Looking at the Overflow Tank
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1 Locate the overflow tank. The coolant overflow tank is typically a clear plastic container that is close to the radiator. To identify it for certain you should look for a tube that connects this tank directly to the radiator.[7]XResearch source
The overflow tank should have a cap right on the top that may or may not say "coolant" on it.
2 Ensure the coolant reaches the "fill" line on the outside of the tank. The overflow tank is made to be relatively clear so that you can see how high the coolant level is inside of it. Look at the sides of the tank to locate the "full" line.[8]X Expert Source Jason ShackelfordAuto TechnicianExpert Interview This should be marked clearly on the tank.[9]XResearch source
The "full" level will not be at the very top of the tank. This tank is designed to have room to allow coolant to move in and out of it as it gets hot and expands out of the radiator and then cools and gets sucked back into the radiator.
3 Make sure the tube between the radiator and the overflow tank is secure. In order for the overflow tank to operate correctly it needs to have a secure path to the radiator so that coolant can move between them. Trace the tube and feel along it between the radiator and the tank. Ensure there are no cracks or breaks and that it is secure at both ends.[10]XResearch source
Advertisement Method 3 Method 3 of 3:
Making Sure Your Coolant is Effective
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1 Inspect the surface of the coolant for signs of an oil leak. Look for an oily film on the surface on the coolant. Coolant can come in a variety of colors, including red, green, blue, and yellow. However, if the surface is dark or has an oily foam on the surface it may mean that there is a leak in your head gasket.[11]XResearch source
This is a serious problem, so you should take your car to a mechanic right away if you see it.
2 Test your coolant's general effectiveness with test strips. After it is used for awhile coolant can lose its effectiveness. In order to ensure that yours is still working, you can use test strips. These are available at most auto-parts stores and from online retailers. To get a reading you simply take off the radiator cap and dip the test strip in the coolant in your radiator. Once you dip your test strip in the coolant it will change color. [12]XResearch source
Each test kit will include a scale for how the test strip reacts and what that means for your coolant. If the coolant no longer provides protection, it will need to be drained and replaced.
3 Use a coolant tester to know the exact protection temperature of your coolant. There are testers available at most auto-parts stores that can be repeatedly used to test your coolant. These are simple tools that are easy to use. You simply take the lid off the overflow tank and stick the hose of the tester in the tank. Then squeeze the bulb on the tester to draw some of the coolant into the tester and read the gauge.[13]XResearch source
The gauge of the tester will move, showing you exactly what temperature the coolant will protect down to.
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Question What should I do if my car's coolant is mixed into the transmission? wikiHow Staff Editor Staff Answer This answer was written by one of our trained team of researchers who validated it for accuracy and comprehensiveness. wikiHow Staff Editor Staff Answer If the coolant has mixed with the transmission fluid, the initial step is to flush out the transmission fluid to remove the contamination. Simultaneously, investigate the source of the leak by bypassing the cooling system and isolating the specific area where the internal leak is occurring. This process aids in identifying the root cause of the issue. Depending on the extent of the damage caused by the coolant contamination, there might be a need to consider rebuilding the transmission to ensure optimal functionality and prevent further complications. Thanks! We're glad this was helpful.Thank you for your feedback. If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow Yes No Not Helpful 0 Helpful 0
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Tips
Radiators should be filled with a 50/50 mix of antifreeze and water. Some comes premixed and some needs to be mixed by hand. However, you should only put straight water into your radiator in an emergency.[14]XResearch sourceThanks Helpful 0 Not Helpful 0
Submit a Tip All tip submissions are carefully reviewed before being published Name Please provide your name and last initial Submit Thanks for submitting a tip for review! Advertisement
Warnings
Coolant is toxic to both pets and humans, so spills should be cleaned up promptly and coolant should be disposed of properly. Thanks Helpful 3 Not Helpful 0
Never open the radiator or add coolant to a hot engine. This could cause you to get scalded and it could damage your engine severely. Thanks Helpful 2 Not Helpful 0
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Expert Interview
Thanks for reading our article! If you’d like to learn more about car maintenance, check out our in-depth interview with Jason Shackelford.
Co-authored by: Jason Shackelford Auto Technician This article was co-authored by Jason Shackelford. Jason Shackelford is the Owner of Stingray Auto Repair, a family owned and operated auto repair shop with locations in Seattle and Redmond, Washington. He has over 24 years of experience in auto repair and services, and every single technician on Jason’s team has more than 10 years of experience. This article has been viewed 50,094 times. 1 votes - 100% Co-authors: 5Updated: February 24, 2025 Views: 50,094 Categories: Vehicle Fuels and Fluids In other languagesJapanese
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Yes No Advertisement Cookies make wikiHow better. By continuing to use our site, you agree to our cookie policy. Co-authored by: Jason Shackelford Auto Technician Co-authors: 5Updated: February 24, 2025 Views: 50,094100% of readers found this article helpful. 1 votes - 100% Click a star to add your vote
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Download Article Co-authored by Jason Shackelford 
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Co-authored by: Jason Shackelford Auto Technician This article was co-authored by Jason Shackelford. Jason Shackelford is the Owner of Stingray Auto Repair, a family owned and operated auto repair shop with locations in Seattle and Redmond, Washington. He has over 24 years of experience in auto repair and services, and every single technician on Jason’s team has more than 10 years of experience. This article has been viewed 50,094 times. 1 votes - 100% Co-authors: 5 Updated: February 24, 2025 Views: 50,094 Categories: Vehicle Fuels and Fluids In other languagesJapanese 
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1 Park the car on a level surface. If the car is not level, for instance if it is parked on a hill, you cannot get a true reading of your coolant level. In fact, if you open up your radiator cap while parked on a hill it could cause coolant to pour out.[1] 
2 Make sure the engine is cool. It is very important for your safety that the engine is cool before you open up the cap on the radiator. The radiator is under pressure and displaces a lot of heat, so it can scald you if the engine is not cool before you open it.[2] 
3 Open the radiator cap. The radiator is at the front of the engine and has a cap on the top of it. In order to remove the cap you will need to press down on it and twist at the same time.[3] In many cases, it will take 2 hands to put enough downward and twisting pressure to get it off because there is a vacuum created inside the radiator.[4] 
4 Ensure the coolant reaches the top of the radiator. When you take off the cap you should be able to see the coolant right at the top.[5] If the coolant is lower or you can't see it, your coolant level is too low.[6] 
1 Locate the overflow tank. The coolant overflow tank is typically a clear plastic container that is close to the radiator. To identify it for certain you should look for a tube that connects this tank directly to the radiator.[7] 
2 Ensure the coolant reaches the "fill" line on the outside of the tank. The overflow tank is made to be relatively clear so that you can see how high the coolant level is inside of it. Look at the sides of the tank to locate the "full" line.[8] This should be marked clearly on the tank.[9] 
3 Make sure the tube between the radiator and the overflow tank is secure. In order for the overflow tank to operate correctly it needs to have a secure path to the radiator so that coolant can move between them. Trace the tube and feel along it between the radiator and the tank. Ensure there are no cracks or breaks and that it is secure at both ends.[10] Advertisement 
1 Inspect the surface of the coolant for signs of an oil leak. Look for an oily film on the surface on the coolant. Coolant can come in a variety of colors, including red, green, blue, and yellow. However, if the surface is dark or has an oily foam on the surface it may mean that there is a leak in your head gasket.[11] 
2 Test your coolant's general effectiveness with test strips. After it is used for awhile coolant can lose its effectiveness. In order to ensure that yours is still working, you can use test strips. These are available at most auto-parts stores and from online retailers. To get a reading you simply take off the radiator cap and dip the test strip in the coolant in your radiator. Once you dip your test strip in the coolant it will change color. [12] 
3 Use a coolant tester to know the exact protection temperature of your coolant. There are testers available at most auto-parts stores that can be repeatedly used to test your coolant. These are simple tools that are easy to use. You simply take the lid off the overflow tank and stick the hose of the tester in the tank. Then squeeze the bulb on the tester to draw some of the coolant into the tester and read the gauge.[13] 
wikiHow Staff Editor Staff Answer This answer was written by one of our trained team of researchers who validated it for accuracy and comprehensiveness.