There is no international standard that maps coolant colour to coolant chemistry. Colour is a dye decision made by each manufacturer, sometimes to signal a product family and sometimes purely for shelf appeal. Two coolants the same shade of green can be completely different fluids.
What the common colours usually mean
| Colour | Usually signals | Notes |
|---|---|---|
| Green | Conventional inorganic (IAT) chemistry | The traditional silicate-phosphate package; shorter service intervals |
| Red / pink | Organic acid technology (OAT) | Long-life; widely used by Japanese and Korean makers |
| Blue | OAT or a maker-specific long-life formula | Common in European vehicles; also used for some G12-family products |
| Yellow / gold | Hybrid (HOAT) chemistry | Often OEM-specific; do not assume it matches a competitor's yellow |
| Purple / violet | Vendor-specific long-life or hybrid | Purely a manufacturer choice |
| Clear / colourless | Ready-to-use water-based product, or an economy grade | Inspect the label carefully — this is where cheap dyed water hides |
The rule that beats colour every time
If you need to top up and you do not know what is in the system, colour will not save you. What does: the vehicle's service record, the original label, or a test of the existing fluid. When none of those exist, the safe move is a full flush and refill with one known product.
What colour genuinely can tell you
- Whether the fluid has changed since it went in. A system filled with red OAT that now looks brown is contaminated or degraded, whatever the label says.
- Whether two drums match. If you are topping up a fleet, matching colour within one brand is a reasonable first filter — as long as you also match the product code.
- Nothing about compatibility across brands. Identical colour is not evidence of identical chemistry, and the two can be incompatible.
How to identify what is actually in the system
- 1Check the service record or the sticker under the bonnet, if the last workshop left one.
- 2Look for the original bottle in the vehicle, or ask the owner what was used.
- 3Test the fluid: pH strips, a refractometer for concentration, and a visual check for oil, rust or sludge.
- 4If the answer is still unknown and the fluid is due, flush and refill rather than guessing.
Use the Coolant Finder
Answer four questions about your market and vehicles and we will point you at the right chemistry and grade.
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