How to top up your radiator coolant

Your car’s engine is a marvel of engineering, tirelessly propelling you from one place to another, day in and day out. But behind the scenes, there’s a delicate balance of temperatures and fluids that keep it running smoothly. One of the unsung heroes in this process is your car’s radiator coolant. It plays a vital role in preventing your engine from overheating, protecting it from the bitter cold, and ensuring the longevity of your vehicle.

Whether you’re a seasoned car enthusiast or a novice driver, understanding how to properly maintain and top up your car’s radiator coolant is a fundamental skill that can save you from costly repairs in the future.

Before you get started, make sure you’re familiar with radiator safety and have purchased suitable quality radiator coolant. At Natrad, we can advise you on exactly the right products and methods to keep your car performing at its highest level.

Watch the video or keep reading for step-by-step advice on changing coolant.

Why should I top up my coolant?

Radiator coolant is a liquid used in the cooling systems of internal combustion engines, such as those found in automobiles, trucks, motorcycles, and various industrial and stationary engines. Its primary function is to regulate and control the temperature of the engine to prevent it from overheating.

To ensure your vehicle operates reliably and efficiently, it’s crucial to regularly check and top up your radiator coolant to maintain the recommended level. Additionally, periodic coolant system flushes and replacements are necessary to ensure the coolant retains its effectiveness and corrosion protection properties over time. At Natrad, our radiator specialists are here to help you keep your engine coolant levels perfect.

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We have the parts and know-how to repair or replace your vehicle's radiator.

What you’ll need

Make sure you have everything you need on hand before getting started. To refill your coolant, you’ll need:

  • Suitable quality coolant
  • Distilled water (if coolant is not pre-mixed)
  • Rags
  • A funnel (optional)

If using an anti-freeze anti-boil coolant concentrate that requires dilution, using a 50/50 mix of water and coolant is usually recommended. Check your owner’s manual to make sure you have the right type of coolant. Using a funnel isn’t essential but helps avoid spillage.

radiator coolant pink

How to refill your coolant

Refilling your coolant is a fairly simple car maintenance task you can do yourself, as long as you follow the right steps. Before you start, always make sure your engine is switched off and cool.

Follow these steps to refill your car’s coolant:

1. Check the coolant level

Your coolant reservoir should be labelled and typically be made from translucent plastic. The outside of the reservoir should be marked with minimum and maximum lines. You can check against these lines to see if you need to refill the coolant.

Refer to your owner’s manual if you are unsure about locating your coolant reservoir.

2. Mix the coolant and water

CAUTION – Mixing or adding the wrong type of coolant may cause an unwanted chemical reaction which can reduce cooling performance or allow corrosion to occur inside your engine.

The coolant you add must be compatible with the coolant already in the system.

If your new coolant is not already pre-mixed, use an empty container to mix equal parts coolant and distilled water to create the 50/50 coolant and water mix that’s usually recommended.

Longer-life coolants are typically of higher quality. Always use high-quality coolants for the best result for your engine.

3. Top off the radiator

If you see a cap on the radiator in your car and you can’t see the coolant level, top it off until you can see coolant at the bottom of the filler neck. There may also be a line indicating the maximum fill level.

4. Top off the coolant reservoir

If your coolant level is low in the reservoir, you can refill it to the max fill line – but do not overfill it. Coolant mixture expands when it is heated. Overfilling it can cause coolant to overflow and damage engine wiring.

Keeping your coolant at the correct level is one of the ways to keep your radiator in good working order.

How much coolant does a radiator take?

The amount of fresh coolant that a car radiator takes can vary depending on the size of the radiator and the specific make and model of the vehicle. Typically, a passenger car with a standard-sized radiator may require around 5-11 litres of coolant to fill the engine’s cooling system.

To get an accurate measurement of how much coolant your car’s radiator needs, it’s essential to consult your vehicle’s owner’s manual. The owner’s manual will provide specific information regarding the coolant capacity for your particular vehicle. The owner’s manual may also specify the recommended type of coolant to use, as there are different formulations of coolant available.

When topping up or refilling the coolant in your car’s radiator, it’s crucial to follow recommendations to ensure proper cooling system performance and to prevent overfilling or underfilling, both of which can lead to cooling system issues.

radiator coolant green

What type of coolant do you need?

There are two major types of coolant: Type A and Type B. Type A contains anti-freeze and corrosion inhibitors, whereas Type B only contains corrosion inhibitors.

Mixing different coolant types can reduce the effectiveness of the corrosion inhibitor and damage your engine. If you are not sure which coolant type is already in your radiator, speak to an expert at Natrad for advice.


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Can I put coolant directly into the radiator?

You can put coolant directly into the radiator, but it’s essential to do so when the engine is completely cool to prevent burns from hot steam or coolant. Open the radiator cap carefully, add the appropriate coolant to the recommended level, and then securely replace the cap. Always follow your vehicle’s manufacturer guidelines for the type of coolant to use and proper maintenance procedures to ensure your engine’s health and safety.

Things to remember

Refilling your coolant is a normal part of car maintenance. But, if you find yourself having to top off your coolant frequently, you may be dealing with a leak issue instead. If this is the case, you need to have a specialist inspect your cooling system. A Natrad cooling specialist can inspect your vehicle to diagnose your issue.

Along with refilling your car’s engine coolant, a periodic flush and cleaning of the system is also required. This can be more difficult than just topping up coolant levels. We recommend having a Natrad specialist take a look at your vehicle’s radiator and trusting them to handle this for you.

Contact us today for more information about radiator repairs, replacements, and safety.