Coolant Types Explained: Zerex G05, G30, G40, Dex-Cool and Asian Formulas

Two coolants of the same colour can be chemically incompatible, and two of different colours can be the same thing from different brands. Dye is a marketing choice. What protects the water pump, the aluminium and the gaskets is the inhibitor package, and that is what the names below describe.

The chemistries

• IAT (inorganic additive technology). The traditional green coolant, protecting with silicates and phosphates. Short service life. Still correct for many older vehicles.
• OAT (organic acid technology). Long-life coolant with no silicates or phosphates. GM's Dex-Cool is the best-known example.
• HOAT (hybrid). Organic acids plus a small amount of silicate for fast protection of aluminium. Zerex G05 is the reference product.
• Si-OAT. A later European hybrid with stabilized silicate. Zerex G40 belongs here.
• P-OAT. Organic acids plus phosphate and no silicate, the formula Japanese and Korean automakers specify.

Which vehicles use what

• G05: many Ford and Chrysler-group vehicles from the 2000s into the early 2010s, and older Mercedes-Benz.
• Dex-Cool type OAT: GM vehicles since the mid-1990s.
• G30: an OAT used by Volkswagen-group and several other European makes of the 2000s.
• G40: later Volkswagen, Audi, Porsche and Mercedes-Benz models.
• Asian phosphated coolant: Toyota, Honda, Nissan, Subaru, Mazda, Hyundai and Kia, each sold under its own name and colour.

Automakers have changed chemistry more than once within the same model line, so treat the list as orientation and confirm against the owner's manual or the cap on the reservoir. The main types are stocked in antifreeze and engine coolant, including Zerex from Valvoline.

What happens when types are mixed

Topping up with the wrong coolant rarely causes instant damage. It dilutes the inhibitors each formula relies on and shortens the life of the fill, and some combinations of old silicated coolant with OAT have been known to form sludge. If you do not know what is in the system, a full drain, flush with distilled water and refill with the correct type is the clean fix.

Concentrate or 50/50

Premix is concentrate already cut with deionized water. It costs more per litre of actual antifreeze but removes the guesswork. If you buy concentrate, mix it with distilled water, not tap water, because minerals in hard water drop out as scale.

• A 50/50 mix protects to roughly minus 37°C.
• A 60/40 mix, more antifreeze than water, protects to roughly minus 52°C.
• Beyond about 70 percent antifreeze, freeze protection gets worse again and heat transfer suffers.

For most of southern Canada 50/50 is enough. On the Prairies and in the North, 60/40 is common. An inexpensive refractometer or float tester tells you what is actually in the radiator before the first cold snap.

Powersports and other systems

Snowmobiles, ATVs and motorcycles often call for silicate-free coolant to protect water pump seals; check the manual before pouring in automotive coolant. RV water lines are a separate matter and use non-toxic propylene glycol plumbing antifreeze, never engine coolant. If the engine is at temperature but the cabin stays cold, the cause is usually not the coolant type; our guide to no heat in the cabin walks through it.

Frequently asked questions

Can I choose coolant by colour?

No. Colour is a dye and is not standardized. Match the chemistry named in the owner's manual: OAT, HOAT such as G05, Si-OAT such as G40, or a phosphated Asian formula.

What happens if I mix two coolant types?

Usually nothing immediate, but the inhibitors are diluted and the service life is shortened. Some mixes of old silicated coolant and OAT can form sludge. A flush and correct refill is the fix.

How strong should antifreeze be for a Canadian winter?

A 50/50 mix protects to about minus 37°C and suits most of southern Canada. A 60/40 mix protects to about minus 52°C. Do not go beyond roughly 70 percent antifreeze.

Should I use tap water with coolant concentrate?

Use distilled or deionized water. Minerals in tap water form scale inside the cooling system.