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Vehicle Fuels and Fluids
How to Check Coolant Level & Add Coolant To Your Car Download Article A guide to filling up your radiator or coolant reservoir Co-authored by Jason Shackelford and Eric McClure
Last Updated: April 3, 2024 Fact Checked
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Checking & Adding Radiator Fluid
|
Inspecting the Coolant Quality
|
Diagnosing Low Coolant Without a Leak
|
Video
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Tips
|
Warnings
|Show more|Show less ARTICLE VIDEO X
This article was co-authored by Jason Shackelford and by wikiHow staff writer, Eric McClure. 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 fact-checked, ensuring the accuracy of any cited facts and confirming the authority of its sources. This article has been viewed 900,488 times.
Your car's radiator is the heart of its cooling system, which also includes a fan, water pump, thermostat, hoses, belts, and sensors. The radiator directs coolant (aka radiator fluid) around the cylinder heads and valves to absorb their heat, returns it to the radiator, and dissipates it safely. To maintain an adequate radiator fluid level, check the coolant level and top it up when necessary. In this article, we’ll show you where to fill the radiator fluid so that you can keep your car running safely.
Where Does Radiator Fluid Go?
Add radiator fluid, or coolant, to your car's radiator. With a cold engine, pop your hood and look for a black (or yellow) radiator cap on top of the radiator. If your vehicle has a coolant reservoir tank, you can add coolant there, instead. Simply remove the cap and add fluid until it reaches the "fill" line.
Steps
Section 1 of 3:
Checking & Adding Radiator Fluid
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1 Park the car on a level surface and raise the hood. Let the engine cool entirely before checking your coolant levels. It’s key to park on a flat surface—if you’re on a hill or angled driveway, the coolant levels will pool up at an angle and give you an inaccurate reading.
Safety Warning: Never leave the engine running when you check the radiator fluid level and do not check the radiator fluid level when the engine is hot—hot coolant can spew out and burn you.
2 Wrap a rag over the cap and remove it. Look for the cap near the top of the radiator or on the coolant reservoir. If your cap isn't labeled, check your owner's manual to find it. The radiator and overflow caps absorb engine heat from the coolant, so using a rag protects you from getting burned.[1]XResearch source
Do you add coolant to the radiator or reservoir? It doesn’t actually matter on most modern vehicles. If you have an overflow reservoir, use that (just because it’s easier to see fluid levels inside). Older vehicles don’t have reservoir caps, so just add coolant to the radiator directly.
Press down on the cap while simultaneously turning it. This will prevent a coolant burst if the system is still pressurized.
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3 Check the radiator fluid level by looking at the “fill” line. Coolant systems don’t normally have a lot of extra room at the top, so the fluid levels should be near the top. If the fluid is more than a few inches from the cap, it’s probably low. Look for the “full” or “fill” line etched into the radiator metal. That is where the coolant should be.
Variation for Modern Cars: If you notice a fill line on your overflow tank (the translucent tank where the excess coolant goes), you can add the coolant there instead of adding it directly to the radiator.
4 Add coolant as needed until it reaches the fill/full line. Use a funnel if you want to prevent spillage. Add the fluid to the overflow tank or radiator until it’s full. Close the radiator cap completely when you’re done.
There are two types of coolant: IAT and OAT. Check your owner’s manual to determine what kind of coolant your vehicle needs.
Almost all coolants on the market today are premixed and labeled “50/50” to indicate they’re 1-part water and 1-part radiator fluid. If you do happen to buy undiluted radiator fluid, mix it with an equal amount of water before adding it to your vehicle.
Advertisement Section 2 of 3:
Inspecting the Coolant Quality
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1 Run a coolant quality inspection if leaks are ruled out. If you’re having overheating issues even though your coolant levels are fine, the quality of your coolant may be to blame. Over time, the ability of your radiator fluid to absorb and dissipate heat declines. So, using a hydrometer to check the freezing and boiling point of the coolant will confirm if you need a coolant flush or not.
If your coolant quality is fine and the levels are correct, your water pump has likely failed. See a mechanic to have the pump replaced.
2 Get a coolant hydrometer and squeeze the bulb. Often marketed as coolant/antifreeze testers, a coolant hydrometer will tell you whether the coolant quality has degraded or not. Squeeze the air bulb on the hydrometer to force the excess air out.[2]XResearch source
3 Insert the hydrometer's rubber tube into the coolant. It doesn’t matter if you do this at the radiator or at the coolant overflow tank, although it’ll probably be easier to use the overflow tank if the coolant levels are visible.
Safety Warning: You must do this with a cold engine. If the engine is hot (or even warm) and you open the radiator or coolant cap, you could burn yourself.
4 Release the bulb to draw the coolant into the hydrometer. Releasing the bulb creates a vacuum that sucks the coolant into the hydrometer. It will float the needle or the plastic balls inside the hydrometer.[3]XResearch source
5 Remove the hydrometer and take your reading. The results will demonstrate the freezing or boiling point level. If your hydrometer uses a needle, the needle should point to either a specific temperature or temperature range. If it uses a series of plastic balls, the number of balls that can float indicates how well your antifreeze protects the engine from freeze-up or boil over. If the levels are too high or low, flush your coolant to replace it with fresh radiator fluid.
A proper freeze point is −35 °F (−37 °C) or lower. An acceptable boiling point is 225 °F (107 °C) or higher.
Advertisement Section 3 of 3:
Diagnosing Low Coolant Without a Leak
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If coolant levels are low but there’s no leak, it’s probably burning away. If you don’t see any drips or puddles under your vehicle but the coolant levels seem to keep dropping, the coolant is probably evaporating in the engine. Coolant smells sweet (a lot of people compare it to candy or maple syrup). If you smell something sugary when you drive, you’ve likely got a coolant leak somewhere. It’s just burning away in the engine bay before it can reach the ground.
You could have coolant issues without a leak. If you worked on your engine recently and opened the coolant lines, air in the coolant lines can get trapped and prevent the coolant from circulating properly. Bleeding the radiator should solve this problem!
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Tips
It is important to the health of your car to change your coolant at regular intervals. Check your owners manual to see how frequently you should change your coolant.[4]XResearch source A good rule of thumb is to change the radiator fluid every 30,000 miles.[5]X Expert Source Jason ShackelfordAuto TechnicianExpert InterviewThanks Helpful 0 Not Helpful 1
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
If you notice fluid underneath your car matching the color of its antifreeze, or notice a sulfurous smell, hear a whistling sound or the temperature gauge goes up and stays up when you drive, take your car in for servicing immediately. Thanks Helpful 56 Not Helpful 42
Most antifreeze contains ethylene glycol, which is toxic to humans and animals. Old antifreeze should be disposed of properly. Ask your local auto body shop where you can safely dispose of antifreeze. Never pour it on your lawn or in a storm drain.[6]X Trustworthy Source Centers for Disease Control and PreventionMain public health institute for the US, run by the Dept. of Health and Human Services Go to source Thanks Helpful 1 Not Helpful 0
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Co-authored by: Jason Shackelford Auto Technician This article was co-authored by Jason Shackelford and by wikiHow staff writer, Eric McClure. 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 900,488 times. 6 votes - 100% Co-authors: 13Updated: April 3, 2024 Views: 900,488 Categories: Vehicle Fuels and FluidsArticle SummaryX
To check your car’s radiator fluid, park the car on a level surface and turn off the engine. Wait until the engine is cool, then pop the hood. Locate the radiator cap, then wrap a rag around the cap and twist it while pressing down at the same time to remove it. Look inside the radiator to make sure the coolant level is near the top or that it reaches the “fill” line inside. Check inside the overflow tank as well—it should be empty or nearly empty. If the overflow tank is full and the radiator is almost empty, your car may need maintenance. If your radiator is low on coolant, use a funnel to add more either to the overflow tank (if your car has one) or directly to the main radiator reservoir. To learn how to test the coolant protection level using a hydrometer, read on!Did this summary help you?YesNo
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Reader Success Stories
Barbara LaMotte
Jun 24, 2017
"To get rid of old antifreeze safely at an auto mechanic's shop where they can dispose of it. Purchase new antifreeze and distilled water using part antifreeze and distilled water to refill radiator."..." more
More reader stories Hide reader stories Share your story If you buy through links on our site, we may earn a commission.
Did this article help you?
Yes No Advertisement If you buy through links on our site, we may earn a commission.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: 13Updated: April 3, 2024 Views: 900,488100% of readers found this article helpful. 6 votes - 100% Click a star to add your vote
Barbara LaMotte
Jun 24, 2017
"To get rid of old antifreeze safely at an auto mechanic's shop where they can dispose of it. Purchase new antifreeze and distilled water using part antifreeze and distilled water to refill radiator."..." more
John Wynne
Apr 19, 2017
"I did not know you still had to uncap the radiator. I thought you just used the overflow container."
Brittany M.
Dec 19, 2016
"Very well explained. Thanks for the help." Share yours! More success stories Hide success stories
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Download Article A guide to filling up your radiator or coolant reservoir Co-authored by Jason Shackelford and Eric McClure 
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Co-authored by: Jason Shackelford Auto Technician This article was co-authored by Jason Shackelford and by wikiHow staff writer, Eric McClure. 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 900,488 times. 6 votes - 100% Co-authors: 13 Updated: April 3, 2024 Views: 900,488 Categories: Vehicle Fuels and Fluids Article SummaryX
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1 Park the car on a level surface and raise the hood. Let the engine cool entirely before checking your coolant levels. It’s key to park on a flat surface—if you’re on a hill or angled driveway, the coolant levels will pool up at an angle and give you an inaccurate reading. 
2 Wrap a rag over the cap and remove it. Look for the cap near the top of the radiator or on the coolant reservoir. If your cap isn't labeled, check your owner's manual to find it. The radiator and overflow caps absorb engine heat from the coolant, so using a rag protects you from getting burned.[1] 
3 Check the radiator fluid level by looking at the “fill” line. Coolant systems don’t normally have a lot of extra room at the top, so the fluid levels should be near the top. If the fluid is more than a few inches from the cap, it’s probably low. Look for the “full” or “fill” line etched into the radiator metal. That is where the coolant should be. 
4 Add coolant as needed until it reaches the fill/full line. Use a funnel if you want to prevent spillage. Add the fluid to the overflow tank or radiator until it’s full. Close the radiator cap completely when you’re done. 
1 Run a coolant quality inspection if leaks are ruled out. If you’re having overheating issues even though your coolant levels are fine, the quality of your coolant may be to blame. Over time, the ability of your radiator fluid to absorb and dissipate heat declines. So, using a hydrometer to check the freezing and boiling point of the coolant will confirm if you need a coolant flush or not. 
2 Get a coolant hydrometer and squeeze the bulb. Often marketed as coolant/antifreeze testers, a coolant hydrometer will tell you whether the coolant quality has degraded or not. Squeeze the air bulb on the hydrometer to force the excess air out.[2] 
3 Insert the hydrometer's rubber tube into the coolant. It doesn’t matter if you do this at the radiator or at the coolant overflow tank, although it’ll probably be easier to use the overflow tank if the coolant levels are visible. 
4 Release the bulb to draw the coolant into the hydrometer. Releasing the bulb creates a vacuum that sucks the coolant into the hydrometer. It will float the needle or the plastic balls inside the hydrometer.[3] 
5 Remove the hydrometer and take your reading. The results will demonstrate the freezing or boiling point level. If your hydrometer uses a needle, the needle should point to either a specific temperature or temperature range. If it uses a series of plastic balls, the number of balls that can float indicates how well your antifreeze protects the engine from freeze-up or boil over. If the levels are too high or low, flush your coolant to replace it with fresh radiator fluid. 
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