Can you mix coolant?

A key part of keeping your engine at the right temperature is using the correct engine coolant. There are so many types and colours available, you may wonder whether it is safe to mix different coolants. In this blog, we will explain everything you need to know about mixing coolant and how to make sure you’re using the right product to protect your engine. 

What is coolant? 

Coolant is a liquid that circulates through your engine and radiator to help control temperature. It is a 50/50 mix of antifreeze and de-ionised water and can be added straight to the coolant reservoir or radiator. 

It performs several important jobs, including: 

• Preventing the engine from overheating 

• Stopping the cooling system from freezing in winter 

• Protecting metal components from corrosion 

• Helping maintain efficient engine performance 

Without coolant, your engine could overheat very quickly, especially during longer journeys or in hot weather. 

 

 What are the different types of coolant?   

There are two main types of engine coolant:   

• Organic Acid Technology coolant (OAT): A long-lasting coolant designed to offer superior corrosion and heat protection, ideal for modern vehicles.  

• Inorganic Additive Technology coolant (IAT): A more traditional coolant often used in older cars, requiring more frequent replacement.  

Some coolants also use a blend of both compounds, known as Hybrid Organic Acid Technology (HOAT), providing a balance between the two. 

 

Are coolant and antifreeze the same thing? 

People often use the terms interchangeably, but technically antifreeze is the concentrated chemical which needs to be mixed with water to create coolant. 

Most modern products sold in shops are either premixed coolant ready to use or concentrated antifreeze that needs mixing with water. In everyday driving conversations, both are commonly referred to as coolant. 

  

Can you mix coolant colours? 

Not always. Coolant colour does not just exist for appearance. Different colours often represent different chemical formulas and technologies. Common coolant colours include blue, pink, green, orange, red, and purple.  

The problem is that colour alone is not a reliable way to determine compatibility. Two coolants that look similar may use completely different chemical additives. Mixing incompatible coolants can reduce protection, damage the cooling system or create sludge inside the engine. 

  

What happens if you mix coolants? 

If incompatible coolants are mixed together, several problems can occur. 

Reduced cooling performance 

Different chemical formulas may not work effectively together, making it harder for the system to regulate engine temperature. 

Corrosion inside the engine 

Coolant contains additives designed to protect metal components from rust and corrosion. Mixing the wrong types can weaken this protection. 

Sludge and blockages 

In some cases, mixed coolant can thicken into a sludge- like substance that blocks pipes, radiators or heater cores. 

Engine overheating 

If coolant flow becomes restricted or less effective, the engine could overheat, potentially causing expensive damage. 

  

Can you top up coolant with water? 

In an emergency, you can temporarily top up with water if the coolant level is dangerously low. However, this should only be a short-term solution. 

Water alone does not provide the same protection against freezing, corrosion and overheating. As soon as possible, the system should be topped up properly with the correct coolant mixture. 

  

How do you know which coolant your car needs? 

The best place to check is your vehicle handbook. Manufacturers specify the correct coolant type for each vehicle. 

 You can also: 

• Check labels on the coolant reservoir 

• Speak to a professional garage 

• Use vehicle registration lookup tools 
• Ask a technician during servicing 

Using the wrong coolant may affect performance and long- term reliability. 

  

Can mixing coolant void warranty? 

In some cases, yes. Modern vehicles often require manufacturer approved coolant formulas. Using the wrong type or mixing incompatible products could potentially affect warranty claims if cooling system damage occurs. This is especially important for newer vehicles and hybrid systems. 

  

How often should coolant be changed? 

Coolant does not last forever. Over time, the protective additives break down, reducing effectiveness. Coolant should be replaced every three to five years or every 30,000 to 100,000 miles, but as recommendations vary depending on type of coolant and vehicle model, it is always best to check your vehicle’s logbook for advice. 

 

What are the signs of coolant problems? 

Cooling system issues should never be ignored because overheating can lead to serious engine damage. 

Common warning signs include: 

• Engine temperature warning light illuminates – indicating that the engine may be overheating  

• Sweet smell from the engine created by coolant leaking into the engine bay  

• Low Frequent low coolant levels requiring top ups could indicate an undetected coolant leak  

• Steam from the engine bay is a major warning sign that the engine is overheating. 

• Poor heater performance – low coolant means the heater struggles to heat the air as it uses heated coolant from the engine in the heater core.  

 

What should you do if you mixed the wrong coolant? 

Don't panic, the system can be flushed out but as the wrong coolant can damage engine components it is best to seek professional advice and do not start the engine or risk driving the car at this stage. 

A garage may recommend testing the coolant condition, flushing the system before refilling with the correct coolant and checking the cooling system for damage or blockages. Acting early will prevent expensive repairs later. 

  

Can coolant affect fuel economy? 

Yes, indirectly. An engine running at the wrong temperature can become less efficient, which may increase fuel consumption and place extra strain on engine components. Proper coolant levels help maintain optimal operating temperatures and engine performance. 

  

Need help choosing the right coolant?   

At Merityre, our qualified mechanics are always happy to help you choose the correct coolant for your car. Whether you need a quick top-up, a full coolant flush, or advice on the best coolant for your car’s make and model, we’ve got you covered. Contact your local Merityre centre today to keep your cooling system running efficiently.   

Visit your local Merityre branch where our specialist mechanics can help. For more information, contact our helpful team today.