Car Coolant Explained: Types, Top-Up, and When to Change

Summary

• Check coolant level monthly: Low coolant can cause overheating and serious engine damage.
• Don't mix different coolant types: Using the wrong type can cause corrosion and blockages.
• Coolant should be changed every 2–5 years: Over time, it loses its protective properties. See our servicing guide for more.

Coolant is one of the most important fluids in your car. Without it, your engine would overheat in minutes — and that means a very expensive repair bill.

Here's what you need to know.

---

What Is Coolant?

Coolant (also called antifreeze) is a mixture of water and chemicals that:

• Prevents overheating: Circulates through the engine to absorb and dissipate heat.
• Prevents freezing: Lowers the freezing point of the water in your system to around -35°C.
• Prevents corrosion: Contains additives that protect metal engine parts from rust and corrosion.

---

Types of Coolant

Type	Colour	Used In	Change Interval
IAT (Inorganic Additive Technology)	Green or blue	Older cars (pre-2000)	Every 2 years
OAT (Organic Acid Technology)	Orange or red	Most modern cars	Every 5 years
HOAT (Hybrid OAT)	Yellow or turquoise	Some European and Asian cars	Every 5 years

Never mix different coolant types. The chemicals can react and form a gel that blocks the cooling system. Always check your handbook for the correct type.

---

How to Check Your Coolant Level

1. Wait until the engine is cold. Never open the coolant cap on a hot engine — the system is under pressure.
2. Find the expansion tank. It's a translucent plastic tank, usually near the front of the engine bay.
3. Check the level. The coolant should be between the MIN and MAX marks on the side of the tank.
4. Top up if needed. Use the correct coolant type, diluted 50:50 with distilled water (or use pre-mixed coolant).

---

Signs of Coolant Problems

• Temperature gauge running high: The engine is overheating. Stop and let it cool down.
• Sweet smell from the engine bay: Coolant has a sweet smell. If you can smell it, there's likely a leak.
• Puddle under the car: Green, orange, or pink fluid under the car is coolant.
• Low coolant level that keeps dropping: You have a leak. Get it checked immediately.
• White smoke from the exhaust: Could indicate a head gasket failure — coolant is leaking into the combustion chamber.

---

Coolant Costs

• Coolant top-up (DIY): £5–£15 for a litre of pre-mixed coolant.
• Coolant flush (garage): £50–£100. Drains the old coolant and replaces with fresh.
• Leak repair: £50–£300 depending on the source (hose, radiator, or head gasket).
• Head gasket repair: £500–£1,500+. This is the worst-case scenario.

---

Coolant and Winter Protection

In winter, coolant prevents the water in your engine from freezing. A 50:50 mix protects down to about -35°C.

• You can test the freeze point with a coolant tester (about £5 from motor factors).
• If the protection level is too low, drain and refill with the correct concentration.
• Never use plain water as a permanent coolant — it freezes in winter and corrodes in summer.

Read our other articles: