Engine Coolant Chemistry Reference: IAT, OAT, Si-OAT (G12evo/G13), and Asian P-OAT Standards
Why coolant dye color is not a specification, how silicate vs phosphate corrosion inhibitors protect aluminum blocks, and refractometer freeze-point testing.
| 50/50 Ethylene Glycol + DI Water | Freeze protection -37 °C (-34 °F) · Boiling point ~129 °C (at 1.1 bar) |
|---|---|
| European Lobrid Si-OAT | Organic acids + silicates (VW TL 774-L / G12evo, MB 325.6) |
| Asian P-OAT (Silicate-Free) | Phosphated organic acid technology (JIS K 2234) |
| Max Glycol Concentration | Never exceed 60% glycol (reduces specific heat capacity) |
1. Silicates (European) vs Phosphates (Asian)
European manufacturers use silicate-enhanced Lobrid coolants (Si-OAT) to rapidly passivate fresh aluminum surfaces, whereas Japanese and Korean manufacturers specify silicate-free, phosphate-buffered coolants (P-OAT) to protect water pump mechanical seals. Mixing incompatible inhibitor packages precipitates gel inside heater cores and radiator micro-tubes.