You've been topping up the coolant for years without replacing it. It's different.

You arrive at the shop for a service and the mechanic tells you the coolant is severely degraded. You’ve been keeping an eye on the level for years, adding fluid when it drops, and thought that was enough.

It’s not.

Topping up and changing are two different things. And confusing the two can be costly.

Why coolant degrades even when the level is fine

Coolant doesn’t wear out like fuel. It doesn’t disappear. But it does age.

Over time it loses the additives that protect it. The most important: anti-corrosion properties. The cooling circuit contains different metals — aluminum, steel, copper — and the coolant acts as a shield between them. When those additives run out, the fluid becomes acidic and starts attacking hoses, the radiator, and the engine block.

Its boiling point also drops. Degraded coolant can boil before expected under high load, which can compromise the engine’s thermal stability under demanding conditions.

The appearance of the fluid is not a reliable indicator either. It can look fine and be completely useless in its chemical properties.

How often you need a complete change

Here there are two different worlds depending on coolant type:

Conventional coolant (green or blue, IAT base): generally every 2 years or between 30,000 and 40,000 km. It’s the most common in older cars.

“Long life” or OAT/HOAT coolant (orange, red, pink, purple): can last between 4 and 5 years or between 100,000 and 150,000 km. It’s the standard in most cars built in the last 15 years.

Check your vehicle’s manual for the exact type and the interval recommended by the manufacturer. Don’t mix different types: they can react with each other and lose effectiveness.

Topping up when the level drops — with distilled water or coolant of the same type — is fine as routine maintenance. But it doesn’t reset the timer on a complete change.

Water-antifreeze mix: not the same in summer as in winter

Antifreeze and coolant are not separate products. Antifreeze is the concentrate; coolant is the ready-to-use mixture. The concentrate is diluted in distilled water in a ratio that determines what temperature range the circuit is protected at.

The standard mix is 50/50 (50% concentrate, 50% distilled water). It protects against freezing down to about -37 °C and against boiling up to about 106 °C.

In areas with very cold winters, you can increase the concentrate to 60-70%. Above that percentage, paradoxically, the protection gets worse.

If you live in an area where winter temperatures drop below -15 °C, check the mix before autumn. Many shops can verify this with a refractometer in less than a minute.

Signs that something is wrong

Preventive changes on schedule is ideal. But there are signs that you can’t wait:

• The expansion tank has sediment, foam, or a dull brown color.
• You find drops under the car when it’s cold (could be a leak, or just condensation from air conditioning in the front area, which is normal).
• The engine takes longer than usual to reach temperature, or it fluctuates a lot.
• The heater stops warming up properly — the heater’s internal circuit shares the engine’s coolant.

None of these signs is definitive diagnosis, but all justify an inspection.

Write down the date and don’t forget it

The real problem with coolant is that, unlike oil, there’s no warning light on the dashboard telling you when it’s degraded. You go years without thinking about it and the circuit gradually loses protection silently.

The simplest solution is to write down the date of your last complete change. With that reference, knowing when the next one is due becomes trivial.

If you use OwnAutoCare to keep your car’s history, you can record the change with date and mileage and set a manual reminder for 2 or 5 years out depending on your coolant type. Without having to remember it yourself.

Coolant maintenance isn’t complicated. It just needs to be done at the right time, not just when the level drops.