Coolant Freeze Point Calculator
Calculate the freeze and boil protection of your coolant mixture.
Find the right antifreeze concentration for your climate.
Coolant (antifreeze) serves two purposes: it prevents the coolant from freezing in cold weather and prevents it from boiling in hot weather. A 50/50 mix of ethylene glycol antifreeze and distilled water is the standard recommendation for most climates.
How Ethylene Glycol Works
Pure water freezes at 0°C (32°F) and boils at 100°C (212°F) at sea level. Adding ethylene glycol lowers the freezing point and raises the boiling point through a process called freezing point depression. The relationship is not linear — there is an optimal concentration beyond which adding more antifreeze actually makes the protection worse.
Freeze and Boil Protection vs. Concentration
| Antifreeze Concentration | Freeze Point | Boil Point (with 1 bar / 15 psi cap) |
|---|---|---|
| 25% antifreeze / 75% water | -8°C (18°F) | 110°C (230°F) |
| 33% antifreeze / 67% water | -17°C (1°F) | 113°C (235°F) |
| 50% antifreeze / 50% water | -37°C (-34°F) | 127°C (260°F) |
| 60% antifreeze / 40% water | -52°C (-62°F) | 133°C (271°F) |
| 70% antifreeze / 30% water | -55°C (-67°F) | 138°C (280°F) |
| 100% antifreeze | -12°C (10°F) | Reduced protection! |
Note: Pure antifreeze provides worse freeze protection than a 70% mix — it must be diluted to function properly.
Recommended Concentrations by Climate
- Mild climate (rarely below -10°C / 14°F): 33–40% antifreeze
- Standard climate (down to -25°C / -13°F): 50% antifreeze (standard recommendation)
- Severe cold climate (down to -45°C / -49°F): 60% antifreeze
- Extreme climate (below -45°C / -49°F): 65–70% antifreeze (do not exceed 70%)
Pre-Mixed vs. Concentrate
Most antifreeze is sold either as a concentrate (100% glycol — requires dilution) or pre-mixed (typically 50/50, ready to use). Always use distilled water, not tap water, to prevent mineral deposits in the cooling system.
When to Change Coolant
Most modern coolants are rated for 5 years or 150,000 km (100,000 miles). Check your owner’s manual. Old coolant becomes acidic and corrodes cooling system components.