Coolant Mixture Calculator
Calculate exactly how much antifreeze and distilled water to add for your desired freeze and boil protection.
System Details
Freeze & Boil Protection Chart
| Antifreeze % | Freeze Point (°F) | Freeze Point (°C) | Boil Point (°F) | Best For |
|---|---|---|---|---|
| 20% | +16°F | −9°C | ~225°F | Very mild climates only |
| 30% | −9°F | −23°C | ~227°F | Mild climates (above 0°F winters) |
| 40% | −20°F | −29°C | ~230°F | Most US/Canadian climates |
| 50% | −34°F | −37°C | ~234°F | Recommended standard — most climates |
| 60% | −62°F | −52°C | ~238°F | Extreme cold climates (Alaska, Canada) |
| 70% | −84°F | −64°C | ~245°F | Extreme cold only — diminishing returns |
| >70% | Protection decreases above 70% | — | Do not exceed 70% antifreeze | |
Why Use Distilled Water?
Tap water contains minerals (calcium, magnesium, chlorides) that deposit as scale on the radiator, water pump, and engine passages. These deposits act as insulators, reducing cooling efficiency. Over time they can clog small passages. Distilled water costs about $1/gallon and eliminates this issue entirely. Never use tap water in a cooling system if you can avoid it.
Never Mix Coolant Types
Mixing green (IAT) coolant with OAT (orange/Dex-Cool) coolant creates a gel-like sludge that clogs coolant passages, destroys water pump seals, and corrodes aluminum components. Always flush the system completely before switching coolant types. When in doubt, use a universal HOAT coolant compatible with most metals and materials.
More Antifreeze Is Not Always Better
Antifreeze is actually a worse heat conductor than water. Above 70% concentration, freeze protection paradoxically begins to decrease and heat transfer efficiency drops significantly. The 50% mix is optimal for year-round use — it provides excellent protection in all but the most extreme climates while maintaining good cooling performance.