As part of an intricate cooling system, your car radiator is an essential component which helps to regulate the temperature of your engine. You may have considered topping up your car radiator with water in the past, but this can actually do real damage to the internal components of your vehicle. When it is time to top up, this blog can teach you exactly what to do so that you can always keep your car in good health. 

You should inspect your vehicle’s coolant levels every 2 to 3 weeks, to ensure that your vehicle has enough fluid to prevent the engine from overheating. If you neglect to replenish these coolant levels regularly - or do so incorrectly - your vehicle may require costly repairs which could have otherwise been avoided. 

After reading this blog post you will know what a car radiator is, how to safely top up your coolant levels, and why you shouldn’t use tap water except in an emergency.


What Is a Car Radiator?

A car radiator is part of a complex engine cooling system designed to prevent the engine from overheating when it burns off fuel. In many modern cars, this cooling system will be made up of the car radiator, a water pump, thermometer and cooling fans. The thermometer will determine the temperature of the engine, directing the water pump to send coolant through the engine as needed. This coolant travels through the engine via hoses, before reaching the radiator where it will be cooled down. The fluid will then head back to the thermometer, ready for when the process repeats itself. When your car radiator is working as it should, it can keep the engine of your vehicle running at the perfect temperature.


When Is It Safe To Put Water In My Car Radiator?

Due to the extreme weather conditions we often experience in the UK, it is unsafe to use solely water in your car radiator. During colder periods water can freeze once the temperature reaches 0°C, and expand into ice crystals within the reservoir. In the warmer months, water can turn into steam as a result of high pressure within the engine. As you can imagine, water can cause real damage in either circumstance. 

When it is time to replenish coolant levels, there are two ways to do so. You can buy engine coolant as a pre-mixed solution, which is usually made up of a 50:50 ratio of distilled water to antifreeze. Alternatively, you can mix a 50:50 ratio of distilled water to antifreeze yourself, so that the antifreeze can regulate the boiling point of the liquid. 

If you choose to take the latter approach, you should bear in mind that the water you use should always be bottled or distilled. Tap water contains minerals which can cause damage to the engine, and may even clog or corrode the radiator pipes. 


How Do I Top Up My Car’s Coolant Levels?

You should top up your car’s coolant levels when the car is cold, to avoid any steam rising from the pipes or car radiator. If you have just used your vehicle, you will need to let it cool down for several hours before you can continue. 

To top up coolant levels, you will first need to lift the bonnet. You may need to undo a catch behind the dashboard to do so - you can refer to your vehicle handbook to find out exactly where this is located on your car. Once the bonnet is raised and fully supported - you may need to use a moveable pole to support its weight - you should find the coolant reservoir cap on top of a clear plastic expansion tank. The words ‘min’ and ‘max’ will be embellished on the side of the container, and you should be able to see some of the existing fluid in the reservoir. 

Unscrew the cap and put this safely to the side - do not leave it somewhere that it could be knocked into the engine. You will by this point know whether you wish to proceed with a pre-mixed coolant, or a 50:50 ratio of distilled water to antifreeze which you will combine yourself. Use a funnel to pour your chosen solution into the container - be careful not to spill any, as antifreeze is highly poisonous to animals. Continue to pour until the fluid reaches the ‘max’ line, then replace and tighten the radiator cap. 

You can now start your engine and let the vehicle idle for 10 minutes. Observe the temperature gauge in your vehicle as you do so, which should rest at the midpoint of the dial when the radiator has enough fluid to cool the engine. 

Note: The order in which you add the water and antifreeze does not matter, as both will combine when you start your vehicle. Just be sure to pour an equal measure of each liquid into the container. 


If you are at all hesitant about replenishing coolant levels yourself, a professional mechanic will be happy to do this for you. When in doubt, it is always best to rely on a skilled garage to do the job right. 


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Can I Use Tap Water in an Emergency?

In an emergency, you can use clean tap water to top up the container. Antifreeze should be added to the container as soon as possible, and you should take care not to overfill the reservoir with tap water as this could damage the larger cooling system. 


Is My Car Radiator Faulty?

You will likely be able to tell that your car radiator is faulty if you notice a visible leak. When your car is stationary, look for a puddle - which could be green or red in colour - beneath your engine. If you notice that your coolant appears to be watery or sludgy, then the problem may be corrosion. Alternatively, a squealing sound from beneath the bonnet could signal that your water pump has frozen if the temperature has dropped recently.

We hope that you feel confident enough to replenish your coolant levels now that you have finished reading this blog. If you are at all concerned about the health of your car radiator, be sure to book a service with an expert mechanic and resolve the issue today. 


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