There is a lot of confusion about mixing coolants. Although this practice seems harmless, it may cause many problems if done incorrectly. Therefore, it is important to understand the similarities and differences between antifreeze products. This can help you decide if certain products can be mixed safely.
Coolants and additives can be differentiated based on key additives, colour, and name.
To these bases, an additive package is added. The technology of these additive packages is categorised into:
Silicate-containing (MEG, IAT) G11
G11 is blue in colour and suitable for older cars, especially those older than 1997. A sodium silicate inhibitor is used in its formulation, which can create a protective layer between the metal surface and the coolant. It has a service life of 2-3 years.
Silicate-free (MEG, OAT) G12/G12+
The G12 coolant is red/pink in colour and is designed for vehicles from 1997 onward. It was developed to meet the needs of aluminium engines and longer service life. This coolant contains no silicates and uses organic inhibitors for lifelong corrosion protection of aluminium and iron alloys, with a lifespan of 4-5 years
The G12+ variant, introduced in 2005, is lilac. The main difference from G12 is its colour; it was created to avoid the unattractive brown colour that resulted from mixing G11 and G12. Its service life is up to 5 years and is compatible with G11.
Organic Inhibitors/Silicate (MEG, OAT) Volkswagen Denomination G12++/G13
G12++ coolant is purple and differs from G12 and G12+ by containing a minimal amount of silicate additives. This formulation achieves a balance between organic inhibitors and silicates, allowing it to maintain the beneficial properties of both types of additives. Its service life is between 5 and 7 years
In 2013, the Volkswagen Group introduced G13, formulated with glycerin. Glycerin is less harmful to the environment than glycol because of its organic origin. This coolant also offers the cooling and protective functions as its predecessors. However, G13 is not the best choice for older cooling systems with a copper/brass radiator and heating block.
G12evo is the latest generation of coolants. It is formulated with ethylene glycol and advanced Si-OAT and has a pink colour. It was introduced in 2018 for VW vehicles with extended service intervals.
Do’s:
Coolants and additives can be differentiated based on key additives, colour, and name.
- Colour
- Types
- Monoethylene Glycol (MEG) is the most commonly used base for automotive coolants. It offers excellent heat transfer properties and provides antifreeze protection down to -37 degrees Celsius, making it the primary component in nearly all coolant technologies in the automotive sector. The downside of it is its toxicity to animals and humans. It also requires responsible disposal and handling.
- Mono Propylene Glycol (MPG) coolants are becoming more popular due to their low toxicity and environmental safety in applications from the food industry, geothermal systems, and electric vehicles.
To these bases, an additive package is added. The technology of these additive packages is categorised into:
- IAT — Inorganic Additive Technology. These coolants are usually bright green in colour, but this can vary. Their formulation includes ethylene glycol (sometimes propylene glycol) + silicate & phosphate additives. It is typically used in older vehicles (before mid-1990) and has a shorter service life due to additive depletion. It is not recommended to be mixed with OAT or HOAT technologies as silicates can react with organic acids, forming gel/sludge.
- OAT - Organic Acid Technology. This type of antifreeze comes in orange, red, pink or purple colours and it is based on ethylene glycol + organic acid inhibitors (carboxylates). It contains no silicates or phosphates, and it is suitable for aluminium engines and modern cooling systems (GM’s Dex-Cool, VW/Audi G12 & G12+).
- HOAT - Hybrid Organic Acid Technology. It can be yellow, turquoise or blue. It has an OAT base and small amounts of silicate or phosphate (IAT) for quick protection. It is excellent for mixed-metal systems (iron + aluminium), and it is typically used in Chrysler, Ford, Mercedes-Benz, BMW
- Si-OAT / P-OAT / PHOAT — Advanced Hybrid Formulas. These are the next-generation OAT hybrids,
- designed for newer engines with specific metallurgy and cooling demands.
| Type | Common Color | Additive Package | Used By |
| Si-OAT | Purple, pink | Silicate + OAT | VW/Audi (G13), Mercedes (MB 325.5) |
| P-OAT | Blue, pink | Phosphate + OAT | Hyundai, Kia, Nissan |
| PHOAT | Blue, pink | Phosphate + HOAT | Toyota, Honda, Subaru |
- Naming
Silicate-containing (MEG, IAT) G11
G11 is blue in colour and suitable for older cars, especially those older than 1997. A sodium silicate inhibitor is used in its formulation, which can create a protective layer between the metal surface and the coolant. It has a service life of 2-3 years.
Silicate-free (MEG, OAT) G12/G12+
The G12 coolant is red/pink in colour and is designed for vehicles from 1997 onward. It was developed to meet the needs of aluminium engines and longer service life. This coolant contains no silicates and uses organic inhibitors for lifelong corrosion protection of aluminium and iron alloys, with a lifespan of 4-5 years
The G12+ variant, introduced in 2005, is lilac. The main difference from G12 is its colour; it was created to avoid the unattractive brown colour that resulted from mixing G11 and G12. Its service life is up to 5 years and is compatible with G11.
Organic Inhibitors/Silicate (MEG, OAT) Volkswagen Denomination G12++/G13
G12++ coolant is purple and differs from G12 and G12+ by containing a minimal amount of silicate additives. This formulation achieves a balance between organic inhibitors and silicates, allowing it to maintain the beneficial properties of both types of additives. Its service life is between 5 and 7 years
In 2013, the Volkswagen Group introduced G13, formulated with glycerin. Glycerin is less harmful to the environment than glycol because of its organic origin. This coolant also offers the cooling and protective functions as its predecessors. However, G13 is not the best choice for older cooling systems with a copper/brass radiator and heating block.
G12evo is the latest generation of coolants. It is formulated with ethylene glycol and advanced Si-OAT and has a pink colour. It was introduced in 2018 for VW vehicles with extended service intervals.
Do’s:
- Use colour as a helpful tool, but ultimately match your coolant by specs
- If you switch brands, flush completely first
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