Engine Coolant & Antifreeze
Engine Oil & Fluids · 6 specs
Direct Answer
Automotive Engine Coolant (standardized under ASTM D3306 and SAE J1034) consists of an ethylene glycol (or propylene glycol) base mixed 50/50 with demineralized water and specialized corrosion inhibitor additive packages. Dividing into classical IAT (Inorganic Acid), modern OAT (Organic Acid Technology / Long Life), and HOAT (Hybrid OAT with silicates/phosphates).
Source: ASTM D3306 (Standard Specification for Glycol Base Engine Coolant) / SAE J1034 / OEM Chemistry Guidelines · Last reviewed Aug 28, 2026
Specs
| Base Liquid Mixture | 50/50 mix of Ethylene Glycol and pure demineralized water (Freeze point: -37°C / -34°F; Boil point: 108°C / 226°F at 1 atm, 129°C / 265°F under 15 psi cap) |
| IAT (Inorganic Acid Technology — Green) | Silicate and phosphate inhibitors (2-year / 30,000-mile service life; standard on pre-2000 vehicles with cast-iron blocks and copper radiators) |
| OAT (Organic Acid Technology — Orange/Pink) | Carboxylate-based inhibitors (5-year / 150,000-mile long-life; GM Dex-Cool, VW G12/G12+, Toyota Super Long Life, Ford Orange) |
| Si-OAT / HOAT (Hybrid OAT — Violet/Blue/Yellow) | Combines organic acids with low-depletion silicates or phosphates (VW G13/G12evo, Mercedes MB 325.5, BMW Blue/Magenta, Asian P-HOAT) |
| Asian P-HOAT (Phosphated HOAT — Pink/Blue) | Uses phosphates instead of silicates (Toyota, Honda, Nissan, Subaru, Hyundai/Kia strictly forbid silicates due to water pump seal erosion) |
| European Si-HOAT (Silicated HOAT) | Uses silicates instead of phosphates (European water has high calcium hardness; phosphates create calcium phosphate scale deposits) |
Why Never to Mix Asian and European Coolants
European automakers (VW, BMW, Mercedes) formulate Silicated coolants (Si-HOAT) and forbid phosphates because hard tap water in Europe precipitates calcium phosphate scale. Conversely, Japanese automakers (Toyota, Honda) formulate Phosphated coolants (P-HOAT) and forbid silicates because abrasive silicate particles wear out mechanical water pump seals. Mixing incompatible coolant chemistries forms gel sludge that plugs heater cores.