# Coolant before winter: can you mix G12 and G13?

*2026-10-04 · autotools*

Before the first frost, check two things: is there enough coolant, and can it handle the cold? When the level in the expansion tank is low, many people grab the first bottle they find. That is where problems start.

## What G11, G12 and G13 mean

These designations come from Volkswagen standards, but they are widely used for other car makes too. They describe the additive chemistry that protects the engine and radiator against corrosion.

* **G11** is an older silicate-based coolant, common in older cars
* **G12 and G12+** are organic additive (OAT) coolants with longer change intervals
* **G12++ and G13** are newer hybrid coolants used in many modern cars

## Why mixing can cause problems

Different additive types are not always compatible. The wrong combination can form sludge or gel that clogs the radiator and heater core and wears the water pump and seals. Corrosion protection weakens even when no visible sludge forms.

Colour is not a reliable guide. Coolants of the same colour can have completely different chemistry, and different manufacturers dye the same type in different colours.

## How to choose the right coolant

* Check the standard or type required in your service book
* Top up with the same type that is already in the system
* If the type is unknown, it is safer to flush the system and replace the coolant completely
* Mix concentrate with distilled water, usually 1:1

## Check the freezing point

If water has been added to the system over the years, frost protection may be much weaker than the bottle says. Frozen coolant can crack the radiator or the engine block.

You can measure the freezing point with a refractometer — a couple of drops is enough. For an Estonian winter, aim for at least −35 °C. Only check the level with a cold engine — never open the cap on a hot expansion tank.

Not sure which coolant your car needs? Ask us — we'll advise based on your vehicle details. See all [coolants](/en/c/coolant) and [refractometers](/en/search?q=refractometer).

## Products in this article

- [ROOKS car refractometer for battery and technical fluids](https://autotools.ee/en/products/rooks-auto-refraktomeeter-akule-ja-tehnilistele-vedelikele) — €26.91
- [Specol G13 coolant, -37 °C, purple](https://autotools.ee/en/products/specol-g13-jahutusvedelik-37-c-lilla?v=GLIKOSPEC%20G13%201L) — €4.41 – €16.11 (from €3.22/l)
- [Motul Auto Cool Optimal G12 coolant, -37 °C](https://autotools.ee/en/products/motul-auto-cool-optimal-g12-jahutusvedelik-37-c?v=AUTO%20COOL%20OPTIMAL%201L) — €9.81 – €40.41 (from €8.08/l)