Engine coolant is the most chemically simple of the automotive fluids and one of the most regulated — it sits alongside the rest of our automotive lubricant formulation range. Eighty-five to ninety-five percent glycol base, three to five percent inhibitor chemistry, deionised water make-up, dye and antifoam — that is the entire formulation. The difficult part is selecting the correct inhibitor technology (IAT, OAT or HOAT) for the target OEM service-fill spec — a task that draws on our additive package development work — hitting the BIS IS 5759 and ASTM D3306 corrosion limits, and delivering colour stability and freeze-point accuracy through 24 months of shelf life. This guide covers the chemistry, treat rates, BIS pass criteria and the Lubechem manufacturing approach for engine coolant in India.
The bulk of an engine coolant concentrate is glycol. Glycol depresses the freezing point of water (the colligative property that gives the coolant its anti-freeze function), elevates the boiling point under cap pressure, and provides the chemical medium for the corrosion inhibitor system to dissolve in.
Mono-ethylene glycol (MEG) is the standard automotive choice. Pure MEG has a freeze point of −13 °C and a boiling point of 197 °C; mixed 50:50 with deionised water it freezes at approximately −37 °C and boils at 108 °C at atmospheric pressure (130 °C at 1 bar gauge under cap). MEG has good heat-transfer characteristics (specific heat ~3.5 kJ/kg·K at 50%) and acceptable viscosity at low temperature. The single significant disadvantage is toxicity — the LD50 in dogs is about 4.4 ml/kg, which has driven the use of bittering agents (denatonium benzoate) in many markets.
Propylene glycol (PG) is used where ingestion risk is a real concern — food and beverage plants, marine applications, dual-purpose HVAC systems, and some defence applications. PG is essentially non-toxic (LD50 > 20 g/kg), but it is more viscous (about 50% thicker than MEG at the same dilution), gives slightly lower heat-transfer efficiency, and costs 30–40% more. For Indian automotive coolant the question rarely comes up — MEG dominates >98% of the market.
Indian MEG supply comes principally from Reliance and IOCL with imported supplement; specification typically calls for >99.8% purity, <0.1% diethylene glycol, and very low chloride. We always test incoming MEG for chloride (target <5 ppm) — chloride contamination is the single most common cause of aluminium pitting failures in finished coolant.
| Component | Function | Typical % (m/m) | Notes |
|---|---|---|---|
| Mono-ethylene glycol (MEG) | Freeze-point depressant, heat-transfer medium | 90–94% | Industrial-grade, >99.8% purity, chloride <5 ppm |
| Deionised water | Solvent for inhibitor salts | 2–5% | Conductivity <5 µS/cm; never use tap water |
| 2-Ethylhexanoic acid (2-EHA) | Aluminium & steel corrosion inhibitor | 1.5–2.5% | Neutralised with KOH on-line |
| Sebacic acid | Aluminium pitting inhibitor | 0.6–1.0% | Long-chain dicarboxylate; works with 2-EHA |
| Neodecanoic / decanoic acid | Cast iron & mild steel protection | 0.4–0.8% | Used in some carboxylate blends |
| Potassium hydroxide (KOH) | Neutralisation to reserve alkalinity | 1.0–1.6% | Target pH 7.8–8.6; RA 6–9 ml |
| Tolytriazole (TTA) | Copper & brass corrosion inhibitor | 0.10–0.20% | Universal across IAT, OAT, HOAT |
| Sodium molybdate (optional) | Cast iron pitting inhibitor | 0.05–0.15% | HDD coolants |
| Silicone antifoam emulsion | Foam suppression | 50–150 ppm | 10% silicone PDMS emulsion typically |
| Dye (fluorescein / rhodamine) | Visual identification | 10–60 ppm | Pre-dissolved in water; never added neat |
| Denatonium benzoate (optional) | Bittering agent against ingestion | 10–30 ppm | Required for export to some markets |
The concentrate above is diluted 50:50 with deionised water at point of use to give the working coolant. Some OEMs and the Indian aftermarket prefer to ship a 33% ready-to-use (RTU) version, which is the concentrate diluted with extra DI water — freezing point about −18 °C, suitable for tropical India where freeze protection is irrelevant and the real job of the coolant is corrosion protection.
| Property | Test Method | IS 5759 Limit | Lubechem Design Target |
|---|---|---|---|
| Glycol content | Refractive index / GC | 93% min (concentrate) | 94–95% |
| Density @ 20 °C | D1122 | 1.110–1.145 g/ml | 1.122–1.130 g/ml |
| Freeze point (50:50) | D1177 | −36 °C max | −37 to −39 °C |
| Boiling point (50:50) | D1120 | 108 °C min | 109–111 °C |
| pH (50:50) | D1287 | 7.5–11.0 | 8.0–8.6 |
| Reserve alkalinity | D1121 | Report | 6.5–8.5 ml |
| Ash content | D1119 | 5% max (IAT) / 2.5% max (OAT) | 1.8–2.2% (OAT) |
| Foam — volume / break time | D1881 | 150 ml / 5 sec max | <50 ml / <3 sec |
| Glassware corrosion | D1384 | See per-metal limits | All metals well within |
| · Copper | D1384 | 10 mg max weight loss | <5 mg |
| · Solder | D1384 | 30 mg max | <15 mg |
| · Brass | D1384 | 10 mg max | <5 mg |
| · Steel | D1384 | 10 mg max | <3 mg |
| · Cast iron | D1384 | 10 mg max | <3 mg |
| · Cast aluminium | D1384 | 30 mg max | <15 mg |
| Aluminium heat-transfer | D4340 | 1.0 mg/cm²/wk max | <0.5 |
| Chloride content | D5827 | 25 ppm max | <10 ppm |
ASTM D3306 is the American counterpart specification — closely aligned with IS 5759 on the corrosion test limits but stricter on some properties. We typically formulate to meet both simultaneously, which expands export opportunity at no formulation cost.
IAT (Inorganic Additive Technology) uses silicate, phosphate and borate inhibitors with a typical 2-year service life. OAT (Organic Acid Technology) uses carboxylates such as 2-ethylhexanoic acid and sebacate with a 5-year / 250,000 km life. HOAT (Hybrid OAT) combines carboxylates with a small silicate or phosphate dose for fast-acting aluminium protection.
Modern BS-VI passenger vehicles — Maruti Suzuki, Hyundai, Volkswagen Group — are typically filled with OAT G12++ or G13 coolants. Commercial vehicles in India lean toward NAP-free HDD chemistry.
Yes, propylene glycol is used where toxicity is a concern — food processing plants, marine applications, dual-purpose HVAC systems near drinking water. PG is less toxic but gives slightly higher viscosity and lower heat transfer than MEG. For automotive engine coolant in India, MEG is the standard base because of cost and heat-transfer efficiency. PG also costs 30–40% more than MEG.
Indian OEMs typically specify a 50:50 MEG:water concentrate giving a freeze point of approximately −37 °C and a boiling point of approximately 108 °C at atmospheric pressure. Ready-to-use 33% MEG variants are sold for tropical regions where freeze protection is not required and the priority is corrosion protection and boil-over resistance — this 33% RTU is the bulk of the Indian aftermarket coolant volume.
BIS IS 5759 is the Indian Standard for engine coolant concentrate. It specifies density, pH, reserve alkalinity, freeze point at 50% dilution, foam, ash content, and corrosion performance on copper, brass, solder, steel, cast iron and aluminium per the ASTM D1384 glassware corrosion test. It is the mandatory specification for branded coolant supplied in the Indian market.
We prepare the complete BIS test data package as part of every coolant regulatory submission.
Colour is a marketing and identification convention, not a chemistry indicator. Volkswagen's G11 (IAT/silicate) is typically blue-green; G12 (OAT) is pink/magenta; G12++ and G13 (Si-OAT) are violet. Indian aftermarket coolants are commonly red, green or blue. The colour is added via a small dose (typically 10–80 ppm) of fluorescein, uranine or rhodamine dye.
Mixing different chemistries can cause inhibitor depletion and gelation, regardless of colour matching — the colour does not guarantee compatibility.
A typical OAT concentrate uses 2.5–4% of an organic acid inhibitor package — usually a blend of 2-ethylhexanoic acid (2-EHA), sebacate and neodecanoic acid neutralised with sodium or potassium hydroxide to reserve alkalinity of 6–9 ml. A small dose of tolytriazole (0.1–0.2%) provides copper/brass protection. Antifoam runs at 50–150 ppm and dye at 10–60 ppm.
Sodium silicate in glycol gels over time unless paired with a silicate stabiliser — typically an organofunctional silane or a polysiloxane stabiliser. The stabiliser is dosed at 10–25% of the silicate weight. Without stabiliser, a HOAT coolant can develop visible gel within 6–12 months on shelf, especially at warm storage. Commercial OAT/HOAT additive packages from BASF, Arteco, Prestone or Old World Industries already include the stabiliser — this is one reason why pre-blended additive packages are preferred to component blending for HOAT chemistry.
Yes — coolant supplied under the ISI mark in the Indian organised market requires BIS licensing under IS 5759. The licence requires factory inspection, batch testing data and an established QC laboratory. We guide clients through the BIS submission for coolant in the same way as for engine oil — the test panel is different but the regulatory process is essentially the same. See our regulatory compliance service.
Share your target market (passenger car, CV, two-wheeler, industrial), chemistry preference (IAT, OAT, HOAT) and production scale. We respond within one business day with a formulation plan, BOM and BIS roadmap.