The ultimate guide to engine coolant

Extreme hot and cold temperatures can severely affect your car, so when the seasons change it’s a great idea to get refreshed on how to care for your engine’s cooling system properly. To maintain a functioning cooling system, you will need to use antifreeze and coolant. However, it can be confusing what the terms coolant and antifreeze mean and how they differ from each other – especially since many people use the terms interchangeably. 

Is antifreeze coolant? Well, antifreeze and engine coolant are similar, but not the same. Antifreeze is a concentrated, glycol-based liquid that must be diluted with water before use – at which point it is referred to as coolant. Alternatively, you can purchase pre-mixed engine coolant, a ready-to-use solution of antifreeze and water.  

Mainly consisting of ethylene glycol, antifreeze is used in a car’s cooling system to enable trouble-free engine operation even in the most extreme, sub-zero weather. Ethylene Glycol prevents coolant liquid freezing within your radiator by lowering its freezing temperature, alongside lubricating the water pump and inhibiting corrosion.  

Engine coolant is a mixture of antifreeze and water, with a common ratio of 50:50. This is because antifreeze works best as a diluted liquid (making it coolant) when combatting temperatures of intense heat. With coolant in your car’s cooling system, the engine can be effectively regulated to the optimum temperature, all year round.  

Antifreeze does not expire, but the additives that prevent engine corrosion do. As such, it’s recommended you replace your antifreeze in line with the manufacturer’s expiry guidelines. 

Additionally, ethylene glycol is toxic to both humans and animals, so make sure to follow the manufacturer’s safety advice and disposal instructions carefully. 

Can you mix pink and blue antifreeze? 

You cannot mix pink and blue antifreeze. An incorrect mixture of coolants could lead to a faulty cooling system and engine damage, so always stick to the mix recommended by your manufacturer.  
 
Can you mix the same type of coolants? 

Always top up your car with the same type and brand of coolant. If you’re unsure which to use, it is always best to follow the manufacturer’s recommendations or contact your nearest garage.  

We do not advise you mix coolants. A common misconception is that you can use colour to identify coolant type, however multiple colours can be used to indicate one type of coolant, so we do not advise using the colour of the liquid solution as an indicator of coolant type.  

The choice of antifreeze and its ready-to-use, water-mixed form, engine coolant, differs between vehicles.

What's the correct antifreeze for my car?

Multiple types of antifreeze are available, with each using a different type of corrosion inhibitor. This is indicated by a coloured dye:

• AT (Inorganic Additive Technology) – Silicates – Green
• OAT (Organic Acid Technology) – Organic Acids – Orange
• HOAT (Hybrid OAT, Phosphate-free) – NAP-free – Turquoise
• HOAT (Hybrid OAT) – Silicates and organic acids – Yellow
• Si-OAT (Silicated HOAT) – Silicates and organic acids – Purple
• P-HOAT (Phosphated HOAT) – Phosphates and organic acids – Blue or pink

If you are wondering which of these types of antifreeze is correct for your car, always check your owner’s manual – every vehicle differs, and using the wrong type of antifreeze will likely cause expensive or irreversible damage to your engine.

What coolant should I use?

Coolants are simply a mix of water and antifreeze, so if you are unsure what coolant you should use, the choice will correspond with the colours and inhibitor types listed above. As with purchasing the correct ready-mixed coolant, always check your owner’s manual before you buy – using the incorrect coolant, or a mix of different coolant varieties, will end up damaging your engine.

As well as displaying which lubricants drivers and fleet operators should use, our TotalEnergies LubAdvisor tool also provides coolant recommendations.

It’s important to make sure that your car has an adequate supply of engine coolant flowing around its cooling system.

That’s why it’s important to check your engine coolant level and top it up from time to time as water evaporates from the solution. Additionally, a low coolant level can be caused by a leak, so checking the level should be a regular task in your DIY car maintenance calendar.

Read our dedicated guide on how to check and top up your coolant.
 

Your car’s coolant system will typically hold around 5 litres of coolant, though this can differ depending on the make and model. You can find out the exact amount from the handbook or your car dealer.

Engine coolants come in a range of bottle sizes so you should be able to get hold of a pack for a full coolant change or quick top-up - whichever suits the maintenance job to hand.

Yes, you can put water in coolant, with some caveats. First, you should only do so in an emergency, such as if you run low on coolant and your car is overheating while on the road. That’s because automotive cooling systems are designed to run on a mixture of 50% antifreeze, 50% water - coolant. If the mixture is off, the performance of the system will be adversely affected.

If you do choose to put water in the cooling system, you should let your car’s engine cool down and make sure to use a cloth to open the reservoir - which may potentially be full of superheated steam. Be sure to pour in the water very carefully too.

You should also only drive your car to your home, and then take it to a garage as soon as possible to have your cooling system looked over for damage and leaks, the water flushed out, and fresh coolant poured back in its place.

It’s also important you use the cleanest water available as well. Distilled is best, however bottled or tap water can be used in absolute emergencies. The more impure the water source, and the longer you keep driving, the more likely that your cooling system will be hampered by mineral deposits.

While the exact timing depends on the make and model of the vehicle, engine coolant typically needs to be changed between two years or 30,000 miles for silicate coolants - whichever comes sooner - or five years or 100,000 miles for coolants designed with specially extended drain intervals.

Coolant needs to be changed because, over time, its composition will change and the ingredients within it will deteriorate. Old coolant won’t protect the engine from overheating as well as new fluid, and other features like corrosion prevention can also be lost over time, putting the cooling system at risk.

To find out the specific coolant drainage interval for your car, check your owner’s manual or talk to your mechanic.

If you check your engine coolant and it is brown and/or bubbling, then it’s likely your cooling system is suffering from rust formation and accumulation. Combustion gases may also be finding their way into the cooling system via the vehicle’s cylinders due to a blown or broken head gasket.

If you encounter either of these issues, you should visit a mechanic. They will drain your coolant, then assess the system and other engine components for damage.

It’s important you don’t continue to drive the vehicle, as even more extensive (and expensive) damage can be done to the cooling system and wider engine if the coolant is brown or bubbling.

If you’ve checked your engine coolant and it keeps disappearing as shown by a lowered reservoir level, puddle beneath your car, or an engine coolant dashboard light that becomes illuminated too soon after you’ve topped up, your cooling system could be leaking.

Coolant leaks can occur throughout the system. There may be a crack in one of your coolant hoses, an issue with your water pump, or your radiator may have a perforation that is allowing the coolant to drip away. The reservoir cap or head gasket may also be broken.

Coolant is toxic to people and pets, and a broken cooling system can put your vehicle at risk of breakdowns, so you need to fix the issue, fast. 

Read our dedicated guide on how to find and repair a coolant leak.

Yes, a coolant leak can cause a ‘check engine’ light, also known as the malfunction illumination light, to show on your dashboard.

That’s because the cooling system is crucial to the health and performance of your engine. If your coolant level is low, then your engine will either heat up above, or cool down below, its operating temperature, affecting its function. This can cause the ‘check engine’ light to show.

That’s not all though. If the temperature rises too high, the Engine Coolant Temperature (ECT) sensor itself can be damaged. This means that simply adding more coolant won’t solve the malfunction illumination light problem, as the engine will understand that there is an error with the ECT sensor. As a result, the ECT may also need to be replaced.

This goes to show just how important it is to keep your cooling system topped up with coolant while on the road.