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Your vehicle is a complicated piece of machinery, and keeping it running smoothly requires periodic inspections and maintenance of its various systems, including your engine’s cooling system and the antifreeze contained within it. You don’t need to be an automotive expert to protect your cooling system against the vagaries of hot and cold weather. What you do need, however, is to put one of the marketplace’s best antifreeze testers in your do-it-yourself vehicle maintenance tool box.

Maintenance is critical when it comes to your engine’s cooling system, which circulates antifreeze—also known as coolant—through the engine to keep it from overheating. But as its name suggests, that antifreeze also prevents freezing in cold weather. Frozen antifreeze can be just as harmful to your vehicle’s engine as excess heat: liquid expands when it freezes, and if that happens inside your engine, it can literally crack the metal and leave you with an inoperable vehicle and an expensive repair bill.

That’s why we’ve compiled this list of the best antifreeze testers. These affordable tools make it easy for you to check the condition of your car’s antifreeze or coolant. Armed with one of these testers and some basic knowledge of how your car’s cooling system works, you can make sure your engine is ready to go no matter the weather.

For more information on the best antifreeze testers, refer to our table of contents.

1. Editor’s Choice: Prestone Antifreeze/Coolant Tester (AF-1420)

prestone antifreeze/coolant tester af-1420

We start our list of the best antifreeze testers with this product from Prestone, a name you’ll surely recognize as a long-time maker of antifreeze and other automotive fluids. The Prestone AF-1420 is a straightforward analog tester that uses a dial to show you the freezing and boiling points of the antifreeze in your engine’s cooling system. To use it, squeeze the bulb, submerge the end of the rubber hose in the antifreeze visible when you remove the radiator cap, and then release the bulb to pull the fluid up into the body of the tester to reveal the condition of the antifreeze.

One side of the tester shows how well the antifreeze will resist boiling in hot weather, while the other side reveals the fluid’s freezing point, which is critical knowledge for winter driving in cold climates. While you’re measuring the antifreeze’s resistance to boiling and freezing, you can use the tester’s clear body to do a visual inspection of the coolant, which can reveal internal cooling system issues like excess acidity and electrolysis.

2. OEMTOOLS Professional Series Antifreeze Tester (24507)

oemtools professional series antifreeze tester

From OEMTOOLS comes this antifreeze tester, an analog tool that uses tried-and-true technology to help you maintain your vehicle, but with an interesting design. Instead of a dial and pointer seen on other popular antifreeze testers, the OEMTOOLS design uses floating discs to show you the condition of the coolant in your car’s engine. Using this recommendation is similar to other analog testers: you squeeze the bulb, insert the tube into your engine’s radiator or cooling system expansion tank until it is submerged, and release the tube to pull antifreeze into the tester’s glass housing.

Once you’ve filled the tester with coolant, you’ll see the discs inside begin to float. The number of floating discs reveals the condition of the fluid: five floating discs means the coolant is in ideal condition. OEMTOOLS says that if its tester’s sixth disc also floats, you need to adjust the ratio of antifreeze to water in your vehicle. This tester’s clear glass body gives you a visual indicator of the condition of the antifreeze and your car’s cooling system and radiator.

3. Best for Cold Climates: SMARTSMITH Antifreeze Refractometer

smartsmith antifreeze refractometer

Next on our list of the best antifreeze testers is this SMARTSMITH tool, which is an optical device that measures the freezing point of engine coolant. Because of that qualification, we recommend this tool only if you live in an area that experiences freezing temperatures for a significant portion of the year. SMARTSMITH’s refractometer works using the principle of refraction to gauge the condition of the antifreeze in your engine. After placing a few drops of coolant on the tool’s daylight plate, you can look through the eyepiece, in which you’ll see a measurement of the fluid’s freezing point.

Though we’re highlighting this tool’s usefulness for monitoring your cooling system’s condition, you can also use it to check your vehicle’s battery by similarly dropping a small amount of fluid from it onto the SMARTSMITH’s daylight plate. Interestingly, if you make your own beer, wine, or honey, you can even use SMARTSMITH’s tool to determine when they are ready for consumption. However, we would recommend buying a second one that you can dedicate to food products.

4. Phoenix Systems Coolant Test Strips (8006-B)

phoenix systems double-ended coolant/brake fluid test strips 8006-b

Here’s the most unique product on our list our of the best antifreeze testers: Phoenix Systems’ coolant test strips offer you a mess-free way to test the antifreeze in your car’s engine by measuring its pH level, or acidity. To use these test strips, all you have to do is dip the correct end of the strip into the coolant, which you can access by removing the radiator cap or opening the cooling system’s overflow tank, if your vehicle has one.

The colored sections on the paper strip will change hues depending on the condition of the coolant. By comparing the resulting color to the chart on the package, you will know within 90 seconds whether the antifreeze is providing adequate protection against freezing or overheating, or whether you need to adjust the mixture or replace the fluid altogether.

Phoenix Systems says its coolant test strips have a shelf life of three years and are compatible with virtually any type of antifreeze you can buy today. These test strips are double-ended: you can also use them to test your car’s brake fluid.

5. ABN Deluxe Antifreeze Tester

abn deluxe antifreeze coolant tester

For the final entry on our list of the best antifreeze testers, we have the ABN Deluxe Antifreeze and Coolant Tester. This is a more traditional tester that you use by drawing the fluid up using a squeeze bulb and then reading the dial that indicates what shape your vehicle’s coolant is in. As with those other squeeze-bulb testers, ABN’s is very simple to use: squeeze the bulb, insert the tube into your vehicle’s coolant, and release the bulb to pull the fluid up into the tester’s clear plastic body.

A needle will show you the freezing and boiling points of your vehicle’s antifreeze, and the see-through housing lets you perform a visual inspection at the same time. The included 5.5-inch tube should be more than long enough to reach the coolant level in your car’s radiator or expansion tank. ABN says its antifreeze tester is compatible with all ethylene glycol-based coolants.

How does your vehicle’s cooling system work?

best antifreeze testers

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Your engine has a water pump that circulates antifreeze through a series of passages in the engine itself so that the fluid can absorb heat from the engine. Then it flows to the radiator, where passing air draws heat out of the antifreeze so that the cooled fluid can go back into your vehicle’s engine and begin the process anew. There’s also a heater core, which is a small radiator built into the climate control system that transfers engine heat into the cabin for winter driving.

Why is it important to periodically test your vehicle’s antifreeze?

After engine oil, antifreeze is the most important fluid in your vehicle. Not only is it designed to keep your engine from overheating, it also prevents freezing in cold weather that can damage—or even destroy—the cooling system or the engine itself.

To do its job, antifreeze and water have to be mixed in the right proportion to provide adequate protection for the environment in which you drive. If that mixture is off or the coolant is old and has lost its protective properties, you could find yourself in need of major engine repairs. As coolant ages, it can become acidic and undergo electrolysis, and either condition can cause accelerated wear on the internal components of your engine and its cooling system.

As the products we’ve highlighted on this list demonstrate, testing your car or truck’s engine antifreeze is a simple and affordable task that makes an antifreeze tester an indispensable part of your car maintenance kit.

How does an antifreeze tester work?

Antifreeze is composed of a specific mixture of chemicals, and an antifreeze tester reacts to those chemicals: the higher their concentration in your vehicle’s cooling system, the stronger the tester’s reaction will be.

The tester will be calibrated to indicate different levels of protection against boil-over—also known as overheating—and freeze protection based on the ratio of coolant to water, or the concentration of the active chemicals in your engine’s antifreeze.

In squeeze-bulb testers, the antifreeze’s chemical makeup causes a mechanical device to float in response to the fluid’s specific gravity. This can be a dial-type mechanism, or a series of balls or discs, either of which you can read against markings that tell you the boiling and freezing points of the antifreeze.

What else do you need to watch for when testing your vehicle’s antifreeze?

When testing the efficacy of your vehicle’s antifreeze, you should also do a visual inspection of the fluid. Most fresh antifreeze is either green or orange. If both the antifreeze and your cooling system are in good shape, it should maintain its color. If the coolant you pull out of the radiator or expansion tank looks muddy, that’s a sign that your vehicle’s cooling system needs to be flushed out and filled with fresh, high-quality antifreeze.


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