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Cold Weather Antifreeze/Coolant: How low can your antifreeze go?

Measuring your antifreeze/coolant’s resistance to cold, and advice on how to best prepare your cooling system for winter weather

The word ‘antifreeze’ is one of the most straightforward terms in the automotive lexicon. Simply put, your automobile’s engine runs hot, and it requires a cooling system to keep it at its optimum operating temperature, regardless of whether you’re driving in the dead of winter or during the dog days of summer. At its most basic, this is accomplished by running coolant through channels in the engine block with its flow regulated by a thermostat and a pump, and its temperature kept under control by a radiator at the front of the car or truck.

Where does ‘antifreeze’ come in? Given that coolant needs to stay liquid in order to do its job, not to mention avoid cracking the engine block open if it were to turn to ice after sitting overnight at well below freezing temperatures, in most climates you can’t simply poor water into your vehicle’s radiator and call it day.



Decades of research have lead to antifreeze/coolant that resists low temperatures while also fighting corrosion and wear inside the cooling system itself. It’s not a ‘set it and forget it’ situation however – antifreeze needs to be periodically inspected, and replaced, as the grind of daily driving takes its toll on the additives that keep your motor running smoothly. This is especially true during the winter months, when your engine is most vulnerable to the cold.

How Does Antifreeze Work?

Antifreeze makes use of ethylene glycol  which is mixed with water in order to both help cool your engine and resist freezing. The most common ratios used are 70 percent water to 30 percent antifreeze for very warm parts of the country, but in colder areas a safer ratio – and the one most manufacturers recommend – is 50:50 antifreeze to water.

What’s interesting about ethylene glycol is that it’s only when mixed with water that it gains its amazing ability to resist freezing. In a 50/50 mix, you’re looking at a mixture that can go down to nearly -50 degrees F before crystallization starts to occur. In a similar way, it also boosts the boiling point of water, providing protection at both ends of the spectrum, and outperforming pure water when dealing with environmental extremes.

Effective Antifreeze, Not Just Glycol

If antifreeze was just made up of glycol and water it would never really wear out – but there’s more to it than that. Preventing corrosion inside your engine’s water channels, as well as its water pump, thermostat, and radiator, is just as important to the longevity of your car as keeping things cool, which means antifreeze manufacturers have to include various additives in order to take into account minerals, scale, and rust. Traditionally, this has been done with phosphates and silicates, otherwise known as inorganic oxides (typically giving antifreeze a green tinge), but inorganic oxides and something called ‘organic additive technology’ are more and more often used in their place, resulting in a wider spectrum of coolant colors.

Each of these additives forms a protective coating over the inside of the cooling system itself, and over time that layer can no longer be replenished, ‘wearing out’ the antifreeze and requiring that it be replaced.

Is Your Antifreeze Ready For Winter

With so many types of antifreeze out there, it’s hard to predict exactly how long the coolant that’s in your car will maintain top-notch cold weather protection. The window is wide, with three to five years, or 50,000 to 150,000 miles being the typical ratings for low-grade to high quality antifreeze. A more common problem, however, is having a mixture that isn’t the ideal 50:50 ratio, which means the freeze point could be higher than you need it to be to survive the winter months.

Fortunately, there are three things you can do to check and see whether your coolant is ready to see you through sub-zero temperatures. Remember – only attempt the following when your engine is completely cold to avoid potential injury from hot.


1. Visually inspect your antifreeze. Open the lid on the overflow tank, which is typically located beside the radiator. Does the coolant look bright and colorful, or is it brown and muddy? The latter indicates that the additives have started to wear out, and that it’s nearing the end of its useful lifespan. It could be time to flush your cooling system and replace it with new antifreeze. Check out PEAK’s How-to Videos and FAQs videos for more information on flushing and filling your radiator.


2. Verify that the system is full Any cooling system only operates at its best when it is topped up. You can add your own pre-mixed, or self-mixed antifreeze and water yourself, to the overflow tank, filling up to the ‘cold’ indicator line. Always read your owner’s manual, check PEAK’s application guide, or consult your local mechanic, to make sure you match the new antifreeze with what’s already inside your vehicle, as mixing different types together can cause problems.


3. Check your antifreeze’s freezing point. You can pick up an inexpensive tool called a hydrometer at any auto parts store that makes use of a float to indicate the freezing temperature of your coolant. The concept is simple: using the small, turkey baster-like bulb on the end of the tool you can suck up a small amount of antifreeze inside of it, and then read where the float sits to show the freezing point of the fluid. The tool will say what ambient temperature it needs to be at to display the greatest accuracy, you’ll want to make sure that the coolant is that temperature, too, and not still warm from driving.


While a 50:50 mix is the most common antifreeze ratio, you may discover that even with a clean and full system your car’s coolant is showing a freezing point that’s higher than predicted temperatures in your area. Keep in mind that wind chill plays a factor, especially if you are parked with the radiator grille facing the brunt of the chilly blast. If your hydrometer is showing a freeze resistance that’s right on the borderline, you might want to consider moving to a more aggressive ratio of antifreeze-to-water. Remember to consult with your mechanic first before making any extreme changes to your coolant and water mix.

russ komarnicki

February 24, 2017

3 thoughts on “Cold Weather Antifreeze/Coolant: How low can your antifreeze go?

  1. Can i buy full antifreeze and run my car without using water in extremely cold weatweather or do i have to use a 50:50 ratio mix

  2. Ordinarily, you should start your car and immediately begin driving. The car can warm-up while you drive.

    EXCEPT when it is sub zero out.

    When it is this cold old, (today it is -4) you should not start driving until the car is warmed up.

    Here is why.

    When the car is cold, the thermostat prevents the water from circulating thru the radiator until that water reaches about 190 degrees. Once that level is reached, the thermostat opens and allows the water to circulate thru the radiator.

    But when it is very cold out and you cause air to move past the radiator (as in driving), it is actually possible to freeze the radiator solid, even if your anti-freeze is OK. (Think “wind chill”) If that happens, the heated water in the engine has no place to go and two things might occur. The engine can overheat (even in the cold) and the hot water suddenly hitting the frozen radiator can cause the radiator to crack. The process is called thermal shock.

    So, avoid super-cooling the radiator by driving and certainly stay off the expressway until the car is warmed-up. Wait at least until heat is being generated inside the car. That means that coolant (water) has started to flow through the radiator. If your car is garage-kept, pull it out and let it warm-up in the alley before driving. Don’t leave the car unattended.

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