Walk down any parts aisle and you will see green, blue, red, pink, orange, yellow and purple coolant. The colour tells you almost nothing — it is a dye, chosen by the blender. What actually matters is the inhibitor chemistry inside, because that decides how long the coolant lasts, which metals it protects and what it may quietly damage.
There are five families worth knowing. Below is what separates them, written for people who buy or specify coolant rather than for chemists.
The five families at a glance
| Technology | Main inhibitor chemistry | Typical service life | Strengths | Watch-outs |
|---|---|---|---|---|
| IAT (Inorganic Additive Technology) | Silicates, phosphates, borates, nitrites | 2 years / ~50,000 km | Forms a protective layer almost immediately | Depletes fastest; silicate can gel and drop out; nitrite is bad for aluminium |
| OAT (Organic Acid Technology) | Carboxylate organic acids (e.g. 2-EHA, sebacate, benzoate) | 5 years / 240,000 km+ | Very long life, low depletion, no silicates to gel | Takes time to build its film, so it protects slowly; some carboxylates attack silicone gaskets |
| HOAT (Hybrid OAT) | OAT carboxylates plus a small dose of silicate and/or nitrite | 5 years / 240,000 km+ | Fast initial protection from the silicate plus long OAT life | Silicate still needs stabilising; formulations vary widely by maker |
| Si-OAT | Silicate plus OAT carboxylates (common in European specs) | 5 years / 250,000 km+ | Protects aluminium water pumps and liners from the first minute | Silicate stability is the engineering challenge; do not top up with plain water repeatedly |
| Borate–organic hybrid | Borate as primary inhibitor plus organic acids | 3–5 years depending on dose | Very stable pH buffering, resists acidification, low depletion, low deposit | Borate is restricted or disliked in a few markets; confirm local requirements |
Why the same car can need different coolant in different countries
Coolant chemistry followed the metals used by each manufacturing region, and old habits stuck.
- North American engines leaned on cast iron and brass, so traditional green IAT with silicates and phosphates was the norm. Modern North American practice has moved to OAT and Dex-Cool style carboxylate chemistry.
- European engines went to aluminium heads, aluminium radiators and frequently aluminium water pumps. Silicate (Si-OAT) protects bare aluminium quickly, which is why European specifications such as VW TL 774 and MB 325.0 rely on silicate plus organic acids.
- Japanese and Korean practice relies on phosphate for aluminium protection, with a low or zero silicate content, because phosphates perform well in the soft water used at the factory.
- Chinese and wider Asian aftermarket production commonly uses a borate-organic hybrid because borate buffers pH very effectively, tolerates variable water quality and keeps deposit levels low.
Colour is not a technology
There is no global colour standard. A red coolant from one blender can be pure OAT; a red coolant from another can be a hybrid. Some markets associate green with IAT and pink with OAT, but nothing enforces it. This is exactly why spec sheets and approvals matter more than the dye.
Which technology should a distributor stock?
It depends on the vehicle parc you serve, not on which chemistry is theoretically best.
- Tropical and subtropical aftermarkets (Southeast Asia, much of Africa and South Asia): a borate–organic or OAT product with a high boil-over margin and no meaningful freeze requirement sells best, because boil-over and corrosion — not freezing — are the real failure modes.
- Cold-climate markets: you need a genuine freeze protection grade, typically -37 °C or -45 °C, built on OAT or Si-OAT depending on the dominant vehicle origin.
- Mixed European vehicle parc: stock an Si-OAT or HOAT product that carries the relevant OEM approvals, because silicate protects the aluminium components those engines rely on.
- Heavy truck and bus fleets: look for a heavy-duty formulation with nitrite or a nitrite-free extended-life package, plus documented cavitation protection for wet cylinder liners.
Use the Coolant Finder
Answer four questions about your market and vehicles and we will point you at the right chemistry and grade.
How to read a coolant specification sheet
When you compare coolant offers, ask for these numbers. They separate real products from repackaged water.
| Parameter | Why it matters | Typical pass value |
|---|---|---|
| Freeze point | Cold-weather protection limit | -37 °C or -45 °C for cold markets |
| Boil point (atmospheric) | Boil-over margin in hot conditions | ≥ 106 °C at 50 % glycol; higher is better |
| pH | Corrosion chemistry stability | 7.5 – 11.0, drifting upward with reserve alkalinity |
| Reserve alkalinity | How long it can neutralise acid | ≥ 5 mL, ideally ≥ 10 mL |
| Chloride | Drives aluminium pitting | ≤ 25 mg/kg |
| Ash content | Predicts deposit formation | ≤ 2.0 % |
| Foaming (ASTM D1881) | Cavitation and pump damage | Foam ≤ 150 mL, break ≤ 5 s |
| Glassware corrosion (ASTM D1384) | Protects six metals at once | ≤ 10 mg per coupon for most metals |
| Cast aluminium heat rejection (ASTM D4340) | Protects aluminium under heat flux | ≤ 1.0 mg/cm² |
A supplier who cannot produce these numbers for a specific batch should not be supplying coolant to a professional market.