Coolant Concentration Mixer
Calculate the exact antifreeze-to-water ratio needed to protect your cooling system at any target freeze point. The wrong mix freezes the block in winter or boils in summer — both kill engines fast.
Coolant Capacity & Type Lookup
Estimate system capacity and select the correct coolant chemistry.
How It Works
Ethylene glycol depresses water's freezing point and raises its boiling point. A 50/50 mix (the universal default) protects to −34°F / +265°F under cap pressure. Higher concentration shifts both points further apart, but past 70% antifreeze the mixture starts to lose heat-transfer capacity.
How to Use This Calculator
- Determine your cooling system total capacity — owner's manual or service manual.
- Pick your target winter low temperature (build in 20°F of safety margin).
- The calculator returns the antifreeze and water volumes to mix.
- Drain the old coolant, mix the new batch outside the radiator, then refill.
- Bleed air from the system per the service manual — overheating after a fill is almost always trapped air.
Worked Example
Reference Table
Freeze and boil points by antifreeze concentration. Note that 100% pure antifreeze does NOT give the lowest freeze point — the eutectic minimum is around 60–65%.
| Antifreeze % | Freeze point | Boil point (15 psi cap) |
|---|---|---|
| 0% (water only) | 32°F (0°C) | 250°F (121°C) |
| 20% | +18°F (−8°C) | 255°F |
| 33% | +4°F (−16°C) | 258°F |
| 50% (universal) | −34°F (−37°C) | 265°F |
| 60% | −54°F (−48°C) | 270°F |
| 70% | −84°F (−64°C) | 276°F |
| 100% (pure) | −10°F (−23°C) — actually rises again | 370°F |
Frequently Asked Questions
Can I mix different colors of antifreeze?
Generally no. IAT (green), OAT (orange/red), HOAT (yellow), and Asian formulations (pink/blue) use different corrosion inhibitor chemistries that react when mixed, forming sludge. Stick to what your manual specifies, or flush completely before switching.
Should I use distilled water or tap water?
Always distilled. Tap water contains minerals that deposit in the radiator and water pump, causing premature failure. Distilled water is $1/gallon at any grocery store.
How often should I flush the coolant?
Conventional IAT (green): every 30 000–50 000 miles. Long-life OAT/HOAT: every 100 000–150 000 miles or 5 years. Always flush if coolant looks rusty, milky, or has visible particles.
What is the pH of coolant — does it matter?
Yes, very much. Healthy coolant is mildly alkaline (pH 8–10). When pH drops below 7, the coolant becomes corrosive and eats aluminum components. Test strips cost $5 — use them before deciding to flush.
Can I use pre-mixed 50/50 coolant?
Yes, and it eliminates the need for distilled water. The premium is small ($3–5 per gallon) compared to a head-gasket failure caused by tap-water mineral deposits.
