Best coolant testers 2026
Now is the time to check if your car’s cooling system is ready for winter
It’s easy to overlook your car’s cooling system, but it’s something you should ignore at your peril. If the coolant inside the vehicle’s radiator or engine block freezes, it can expand and cause the metal to crack, often with disastrous consequences.
Anti-freeze, which is also known as coolant, gradually deteriorates over time due to repeated heating and cooling cycles within an engine. As it ages, vital additives that prevent corrosion break down, reducing the fluid’s effectiveness. Also, contaminants such as rust can accumulate, further compromising the anti-freeze’s ability to regulate temperature.
Checking and replacement are essential to maintain optimal engine health, and with a simple anti-freeze tester costing from less than £8, you can ensure your anti-freeze will stay liquefied – but which tester is best?
How we tested
We brought together seven popular anti-freeze testers and tried them out in two scenarios. The first was to test each in a bottle of freshly opened Prestone coolant and rated to minus-37 degrees Celsius.
Then we dipped the tester into the expansion tank of a car that we knew hadn’t had a full service since 2021 and had weakened coolant, to see how the testers each rated its strength. Ease of use and price were also assessed.
BGS DIY 1822 Anti-freeze Tester
- Price: around £7.82
- Anti-freeze sample: -37°C
- Car sample: -7°C
- Rating: 5.0 stars
- Contact: amazon.co.uk
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2023 Mercedes
AMG A45
24,551 milesAutomaticPetrol2.0L
Cash £38,995
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Q4 Sportback e-tron
43,103 milesAutomaticElectric
Cash £20,080
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EQB
47,231 milesAutomaticElectric
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Model Y Premium
29,934 milesAutomaticElectric
Cash £23,995Available from multiple stores on Amazon and designed in Germany to TüV standards, the BGS tester is simple and easy to use. You insert the attached tube into the sample coolant, give it a squeeze and then wait for the chamber to fill with liquid. After a few seconds, the dial moves to show the depth of temperature to which your coolant protects.
On the fresh anti-freeze, it showed full protection to -37°C, exactly as quoted by Prestone. It showed the cooling system on our car to be safe down to -7°C, proving it’s certainly due a coolant change. At less than £8, BGS is a great addition to your toolbox and a genuine bargain.
Sealey Twin-rotor Anti-freeze Tester
- Price: around £26.95
- Anti-freeze sample: -28°C
- Car sample: -5°C
- Rating: 4.5 stars
- Contact: sealey.co.uk
If you want a workshop-quality product, then the Sealey Twin-rotor Anti-freeze Tester feels like it’s made to last. It seems more durable than our winner, but not enough to justify paying three times as much for a product you’ll probably only use once a year.
It operates in a similar way to the BGS – squeeze the bulb, let it fill up and take a reading from the dial, although we do think it under-read slightly, suggesting protection of down to -28°C for the fresh Prestone coolant and -5°C for our car radiator. Still, better a cautious reading than one that gives a false sense of security.
Halfords Anti-freeze Tester
- Price: around £13.99
- Anti-freeze sample: -32°C to -37°C
- Car sample: +5°C to -15°C
- Rating: 4.5 stars
- Contact: halfords.com
Pipette-type readers are generally less accurate than the rotary style ones, because they give temperature protection ratings within a range rather than a fixed number.
With this Halfords one, you count the number of coloured discs that float above the test marker once you’ve filled it with sample fluid. It’s very easy to use and unlike some of the other disc-type testers we evaluated, it didn’t drip and leak fluid in use.
The readings the Halfords’ tester gave during both parts of our evaluation were broadly in line with what we expected, and the tool felt sturdy in use.
Silverline Anti-freeze Tester
- Price: around £8.10
- Anti-freeze sample: -32°C to -37°C
- Car sample: -6°C to -16°C
- Rating: 3.5 stars
- Contact: screwfix.com
The Silverline tester is so similar in appearance to the Halfords one (left) that we did wonder if they were the same product but rebranded. However, the Halfords tester felt more precise in use and gave us a more stable reading in less time. Also, when we took a sample with the Silverline, the extraction tube tended to drip and make a mess. Its readings seemed accurate, though.
Sealey Tube-Type Anti-freeze Tester
- Price: around £11.95
- Anti-freeze sample: -20°C
- Car sample: 0°C
- Rating: 3.0 stars
- Contact: sealey.co.uk
Unlike the other pipette-type testers here, the Sealey uses a scale rather than a series of floating discs to give a reading.However, when tested on our vehicle it didn’t register protection below zero at all, and for the fresh antifreeze it gave a reading of -20°C protection, which is barely half of the product specification. Sealey’s tester will tell you if your coolant system is fit to face a British winter, but not especially accurately.
Simply Anti-freeze Tester
- Price: around £10
- Anti-freeze sample: -26°C to -31°C
- Car sample: +5°C to -15°C
- Rating: 2.0 stars
- Contact: rpdistribution.co.uk
Similar in design to the Silverline and Halfords testers, the Simply tester would have scored more highly had it not been dribbling coolant all over our floor and subsequently our engine bay, despite it supposedly holding the fluid in a vacuum.
It also under-read the protection offered by the fresh coolant, with one of the discs in its chamber not moving at all, despite being given a few gentle taps. The Simply is easy to use, though.
Draper Anti-freeze Tester
- Price: around £10.50
- Anti-freeze sample: -24°C
- Car sample: n/a
- Rating: 1.0 stars
- Contact: drapertools.com
We’re normally big fans of Draper tools, but this didn’t win us over. Its scales for testing hot and cold engines are handy, but it won’t read any level of protection above -12°C, so couldn’t suggest any protection for our car at all. After we’d used it once, we went to try it again and found the inner glass tube had shattered, even though we hadn’t been rough with it. The lifetime guarantee means a replacement was covered.
Verdict
- BGS DIY 1822 Anti-freeze Tester
- Sealey Twin-rotor Anti-freeze Tester
- Halfords Anti-freeze Tester
We found the rotary-dial-type testers to be the most effective products here, while the Halfords was the best of the pipette testers.
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