How to Test Antifreeze

Maintaining the right balance of antifreeze in your vehicle is key to protecting your critical engine components from extreme temperatures, damage, overheating, and corrosion, and also prevents freezing in cold temperatures that could lead to block or cylinder head damage. Also known as coolant, antifreeze regulates engine temperature to prevent overheating as well as limiting the risk of freezing in cold temperatures. Over time, antifreeze can break down or become contaminated or diluted, which could cause boilover, corrosion, or allow freezing to occur inside the engine. Testing antifreeze helps you discern its freezing and boiling points, indicating the overall health of the antifreeze in your system. This can help you make a decision on whether or not your vehicle’s antifreeze is offering enough engine protection, and whether an antifreeze flush and fill or antifreeze ratio correction may be appropriate. Our step-by-step video shows how to test antifreeze in most vehicles, but check your owners manual for coolant testing specifics as well as the location of the coolant reservoir or radiator cap. Whether you're prepping for summer heat or winter cold, testing your coolant is a simple step to make sure your engine stays running cool year-round.

Tools & Materials List
Step by Step Instructions
Additional Resources

Tools & Materials

Safety Eye Glasses Safety Glasses
Protective Gloves Nitrile Gloves
O'Reilly Antifreeze and Coolant Antifreeze & Coolant
Prestone Antifreeze Tester Prestone Antifreeze Tester

Steps to Test Your Antifreeze

Our expert opens the hood of a parked Nissan Rogue Sport.

Let Your Engine Cool

Make sure your vehicle’s engine has been off for a few hours, or overnight. Your cooling system becomes pressurized when hot, and opening it before it has cooled can cause antifreeze to spray out and cause injury.
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In two images, our expert uses the back of their hand to gauge the warmth from the cooling system and opens the radiator cap.

One way to ensure your system is cool is to feel the radiator or hoses with the back of your hand. Once you’re sure it’s safe, remove the radiator cap or coolant reservoir cap.
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Our expert uses a flashlight to inspect the coolant level.

Inspect Coolant Level

Use a flashlight to visually inspect the coolant level and condition. If your vehicle doesn’t have an overflow tank, the level might be a little lower to allow for expansion at operating temperature.
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A close shot of the Prestone Coolant Tester with blue coolant in it.

Check Antifreeze Consistency

Antifreeze comes in several different colors, but its appearance should be slightly transparent.

• If your antifreeze looks milky, or has particles floating in it, the system may need to be drained and flushed to remove the contamination. If the problem persists, it could indicate an issue like a blown head gasket or other problems that may require professional service.

• If the coolant looks clear and clean, the next step is to check the coolant-to-water ratio. Your vehicle’s manufacturer will specify the ratio of water to coolant that your engine needs, and you can buy a simple tester to let you know whether that ratio is where it should be. Be sure to read the instructions for your tester before use.

Do It Right: Your tester may include color-coded balls or a needle to show the ratio and protection level.

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In three images, our expert uses the bulb and tube attached to the coolant tester to check the freeze and boil-over point.

Determine Freeze and Boil-Over Points

Use the tube and the bulb of your tester to draw some coolant into the tester then use the gauge to determine freeze and boil-over protection levels.

• If the coolant shows a freeze point of greater than -34 degrees or a boil-over point of less than 265 degrees Fahrenheit, additional service or adding pure, undiluted coolant to correct the ratio may be needed. Too much coolant in the ratio can also cause a low freeze point, and it may need to be diluted.
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In two images, our expert pour fresh coolant into the cooling system.

Add New Coolant

Top off the coolant level with the appropriate type and mixture if it is low but passes the test or add pure antifreeze or distilled water if needed to balance the ratio.
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Our expert replaces the cap to the cooling system.

If for any reason your coolant needs to be completely drained and refilled, you can find an instructional video here, on our How-To Hub.
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Additional Resources

Antifreeze being poured

Is All Antifreeze Created Equal? Exploring the Types of Antifreeze
Smoke rising from vehicle

What Causes a Car to Overheat?
Expert replacing hoses

How to Replace Radiator Hoses

Checking your coolant health is essential for preventing overheating, freezing, and protecting your engine against damage. Regular antifreeze checks are key to preventing engine damage from extreme temperatures. O’Reilly Auto Parts has the coolant testers, antifreeze, refractometers, funnels, and more to help you maintain your vehicle’s cooling system and keep your engine running and cool in any season. Visit our How-To Hub for helpful articles including the types and colors of antifreeze, what causes a car to overheat, cooling system basics, and much more to help you protect and extend the life of your vehicle.

The automotive repair work depicted in this series is performed under the direction of the manufacturer of the product featured. Prior to undertaking any of the demonstrated repairs on your vehicle, we suggest you consult with a certified mechanic or another professional who can adequately advise you of the proper repair or remedy required. O’Reilly Automotive Stores, Inc. and its affiliates (“O’Reilly”) disclaims any responsibility for injury or damage resulting from a viewer’s attempt to recreate the repairs shown in this series.