What is antifreeze?
Antifreeze is a chemical additive that lowers the freezing point and increases the boiling point of the fluid in your car's coolant system. This prevents the coolant from freezing in cold weather and helps to stop the engine from overheating. It’s an essential product that every vehicle needs to run smoothly and safely.
- What does antifreeze do?
- Is coolant the same thing as antifreeze?
- Where does antifreeze go?
- Can you mix pink and blue antifreeze?
- Can you put too much antifreeze in a car?
- What type of antifreeze is right for my car?
- How often should you top up your car with antifreeze?
- How to top up antifreeze
The fluid in your car's coolant system is water based, and that means it’s at risk of freezing in sub-zero temperatures. Antifreeze contains a chemical that lowers the freezing temperature of the coolant fluid in your car, typically to around -37.5°C.
But antifreeze doesn't just protect your car in very cold weather: it stops the coolant system from overheating, too. Your engine gets extremely hot, and the coolant system circulates coolant through the radiator to stop the engine from overheating. Antifreeze increases the boiling point of the coolant to around 106°C, which stops it from boiling off and evaporating when things get very hot. This in turn allows the engine to maintain a safe operating temperature.
Many antifreeze products also contain additives and inhibitors that help to prevent corrosion inside the coolant system. This keeps it in good condition and helps to prolong the lifespan of the engine as a whole.
Coolant liquid is a mixture of water and antifreeze. So, while engine coolant does contain antifreeze, they're not one and the same thing, as the antifreeze is diluted with water. The exact concentration of antifreeze in the coolant will vary depending on the make and model of car, but in most vehicles the recommend level is a 50/50 split of antifreeze and water.
Antifreeze is sold both as an undiluted concentrate, or as a premixed coolant fluid which contains a 50/50 mixture of antifreeze and water. If you buy concentrated antifreeze, you'll need to mix it with water yourself, while ready-mixed products can go straight in the coolant tank.
Antifreeze is added to the coolant reservoir, a plastic tank that is mounted in the engine bay on most makes and models of vehicles. There should be a cap somewhere on the top of the tank, which is where new coolant is added. Your car owner's handbook or Haynes manual can help you locate the coolant reservoir in your vehicle.
When topping up the antifreeze, you should remember that you should never add pure, undiluted antifreeze to the coolant tank straight from the bottle, as this could damage the cooling system and even cause the engine to overheat. Antifreeze should always be mixed with water according to the instructions on the packaging until it meets the coolant liquid concentration recommended by your car manufacturer.
You should never mix pink and blue antifreeze, or any two different kinds of antifreeze. The chemical formulations may be different, which could cause a reaction that would reduce the effectiveness of the antifreeze. In the worst-case scenario, it could even damage the cooling system. Using one single brand and type of antifreeze is the safest course of action.
If for some reason you can't find exactly the same type of antifreeze as you currently have in your car, then we would advise draining and flushing the system before refilling it with a fresh coolant mixture.
Yes, it is possible to put too much antifreeze in your car. Although you might think that a higher concentration of antifreeze would make the coolant less likely to freeze, it can actually have the opposite effect: pure ethylene glycol (the most common type of antifreeze) will freeze in temperatures lower than around -17.8°C. When mixed with water, the freezing point drops to around -37.5°C.
For optimum performance, you must use a mixture of both antifreeze and water in your car's coolant system — a 50:50 split is recommended for most makes and models, although you can check the exact level in your owner's manual. So, you don't want the level of antifreeze in your coolant liquid to exceed the recommended concentration.
You can find an antifreeze that is suitable for your car by entering your registration on our antifreeze page or by consulting your owner's manual. Most modern cars require a silicate-free, organic acid technology (OAT) type of antifreeze. Cars manufactured before 1998 will normally need a product that isn't OAT-based and does contain silicate.
There are a few other things to consider when choosing the best type of antifreeze for your vehicle:
- Concentrate vs coolant: Antifreeze is usually sold as a concentrated solution, which must be mixed with water before use, or as a coolant solution containing 50% antifreeze and 50% water. Premixed products are more convenient if the concentration is suitable for your vehicle.
- Ethylene glycol vs propylene glycol: In most antifreeze products, the main chemical ingredient is ethylene glycol or propylene glycol. Propylene glycol is less toxic, which means it is safer and more environmentally friendly. However, ethylene glycol lowers the freezing point and increases the boiling point of coolant more dramatically, which makes it a better option for extremely cold or hot climates.
- Extra additives and inhibitors: In addition to the chemical compounds mentioned above, some formulas include other additives and inhibitors which help to stop the metal parts of your car coolant system from corroding. This can help to prolong the lifespan of your coolant system and engine.
To top up your car's antifreeze, you'll need the following products and tools:
- Antifreeze: This should be the right type for your car and the climate conditions where you live. You can use either a concentrated antifreeze, or a premixed coolant fluid at the right concentration for your car.
- Clean water (if using a concentrated antifreeze): Ideally, you should use water which has been boiled and left to cool to dilute concentrated antifreeze. This ensures no harmful bacteria make it into your coolant system, helping prevent corrosion and increase the lifespan of the system.
- A mixing vessel (if using a concentrated antifreeze): This should preferably be a plastic fuel carton or tank with a large enough capacity to mix at least a few litres of coolant. Using a mixing vessel or tank with measurement indicators on it will also help you to get exactly the right concentration.
- Funnel: This will make it much easier to add the fluid to the tank.
- Protective goggles and gloves: Most antifreeze products (particularly those containing ethylene glycol) are toxic, so you really don’t want to get them on your skin. As well as protective goggles and gloves, you should wear full-length sleeves to ensure no skin is exposed on your arms. If any antifreeze does come into contact with your skin, wash it thoroughly under a tap as soon as possible. If you accidentally swallow some or get some in your eyes, seek medical attention immediately.
- Cleaning cloths and towels: For wiping away spills and cleaning the cap.
Before you begin, remember that you should never attempt to top up the coolant when the car is still hot, as this could cause burns or scalds. Always wait until the engine has cooled down completely before attempting to do this.
In some instances — for instance, where the coolant fluid is several years old, or you suspect that the system has been contaminated with dirt or another type of fluid — it may be better to drain the system and refill it with fresh coolant. You can learn all about how to do this in our guide to flushing the radiator and cooling system.
- Put on your protective gloves and goggles. Then, if you are using a concentrated antifreeze, mix it with the water using your mixing vessel or empty tank, being sure to follow the instructions on the packaging and in your car owner's manual. If you are using a pre-mixed coolant solution, you can skip this step and go straight to step 2.
- Open and secure the bonnet and cover the coolant reservoir cap with a clean cloth. Then, slowly unscrew the cap. Pressure might have built up inside the reservoir over time, so you'll want to work slowly and hold the cap down firmly to ensure that it doesn't fly off. Once the cap is removed, put it to one side.
- Place the funnel into the coolant reservoir opening. Then, take the antifreeze and water mixture (or the premixed coolant, if this is what you're using) and pour it carefully into the reservoir until it reaches the desired level. You should never exceed the maximum markings on the side of the tank.
- Replace the cap and tighten it until secure. If any of the coolant has spilled around the tank, mop it up with a clean cloth. Lower the bonnet, and you're all done!
You can find out how often you should be topping up the antifreeze in your car by consulting your owner's handbook. Most manufacturers recommend this is done every 2–3 years or so, although these days some vehicles come with "lifetime" blends of coolant that never need to be topped up. So, be sure to check what’s right for your car before taking action.
It's sensible to top up your car with antifreeze at the start of the winter where possible, to ensure that your car's coolant system won't freeze over when the mercury drops. For more tips and advice on getting your vehicle ready for colder weather, take a look at our winter car checks guide.
You may also need to top up your car with extra coolant if the level is running low. You can tell if the system is running low by seeing whether it falls between the minimum and maximum marks on the side of the coolant reservoir — if it’s near the low or minimum mark, it’s a sign that it's time to add some more coolant fluid. Always check this when the engine is cool, as this will ensure the reading is accurate. If you've noticed that the level keeps dropping despite repeated top-ups, you may have a leak on your hands. Read our guide to spotting and repairing a radiator leak to learn how to handle this.
Please note that the compounds in the antifreeze gradually degrade over time, which reduces the effectiveness of the coolant. How fast this degradation will take depends on all sorts of factors, and the only way to check the quality and effectiveness of the antifreeze inside your vehicle is by using a coolant hydrometer. However, assuming you stick to the recommended top-up intervals stated in your owner's manual, you can probably safely assume that the antifreeze is providing effective protection.
Here at GSF Car Parts, we have a fantastic assortment of antifreeze to suit all makes and models of car, including both concentrated products and premixed coolant fluids. All of our antifreeze is sourced from trustworthy automotive brands, so you can count on it keep your cooling system running smoothly, as well as helping to increase the lifespan of your radiator and engine. We also have cooling system cleaner that might be of interest to you.
If you’re interested in learning more about keeping your car in great condition, be sure to take a look at our auto knowledge hub, where you can find a wealth of expert advice on everything from changing a tyre to removing bodywork scratches at home.