Engine Coolant Explained: Colors, Types, and What You Should (and Shouldn’t) Mix

Engine coolant isn’t just colorful fluid—it’s a vital part of your vehicle’s health. From preventing overheating to protecting metal components from corrosion, the right coolant plays a crucial role in long-term engine performance.

But with so many colors and types on the market—green, orange, pink, yellow—it’s easy to get confused. Which coolant should you use? Can you mix different types? What do the colors really mean?

This guide breaks it all down.

Why Coolant is Better Than Water

While some might be tempted to use plain water in their cooling systems, coolant offers several key benefits:

• Higher Boiling Point: Coolant resists boiling at high temperatures, especially under pressure.
• Lower Freezing Point: Prevents the system from freezing and expanding during cold weather—unlike water, which can crack your engine block.
• Corrosion Protection: Coolants are formulated with inhibitors that prevent rust, corrosion, and scale buildup.
• Lubrication: Helps lubricate the water pump and seals within the cooling system.
• Reduced Foaming: Coolant foams less than water, which ensures better circulation and heat transfer.

The Ideal Coolant Mix

The standard mix is:

• 50% coolant
• 50% distilled water

In extremely cold climates, you can go up to 60% coolant / 40% water, but avoid higher ratios, as they can reduce cooling efficiency.

The 3 Main Types of Engine Coolant

Now, let’s explore the three primary coolant technologies—and how color ties into them.

1. IAT (Inorganic Acid Technology) – Green

Used from the 1920s to the 1990s, IAT coolant was the industry standard for decades.

• Color: Green
• Contains: Silicates and phosphates
• Service Life: ~2 years or 30,000 miles
• Vehicles: Older domestic cars (GM, Ford, Chrysler)
• Key Feature: Strong corrosion protection, but short lifespan

Ideal for classic cars or older vehicles that originally came with green coolant.

2. OAT (Organic Acid Technology) – Orange

OAT coolant gained popularity in the mid-1990s and is still widely used today.

• Color: Typically orange (sometimes dark red or pink)
• Does NOT contain: Silicates or phosphates
• Service Life: ~10 years or 135,000+ miles
• Vehicles: GM (Dex-Cool), Volkswagen, Honda, Nissan, Toyota, Mitsubishi
• Key Feature: Long-lasting corrosion protection via organic acids

Do not mix OAT coolant with older IAT types—it can cause sludge, reduce effectiveness, and damage radiators with lead soldering.

3. HOAT (Hybrid Organic Acid Technology) – Yellow or Turquoise

As the name suggests, HOAT combines elements of both IAT and OAT coolants.

• Colors: Yellow, turquoise, gold, or even blue
• Contains: Organic acids + limited silicates (no phosphates)
• Service Life: ~5 years or more
• Vehicles: Ford (yellow/gold), Chrysler, BMW, Volvo, Tesla, Mini, European brands
• Subtypes:
  • Phosphated HOAT (P-HOAT) – Common in Toyota, Honda, Hyundai, Kia; typically pink or blue
  • Silicated HOAT (Si-OAT) – Found in Mercedes-Benz, VW, Porsche; usually purple

Color isn’t always reliable—always check your owner’s manual or radiator cap for the correct coolant type.

Can You Mix Coolant Types?

Generally, No

Mixing different coolant chemistries (IAT, OAT, HOAT) can cause:

• Reduced corrosion protection
• Sludge buildup
• Reduced lifespan (back to 2 years)
• Potential internal engine damage

Exception: Universal Coolants

Brands like Prestone “All Makes, All Models” are designed to be compatible across coolant types for topping off your reservoir.

However:

• Use only in emergencies or minor top-offs
• Best practice: Drain and flush your system completely before switching types

To switch coolants safely:

1. Fill with distilled water
2. Run engine briefly
3. Drain and repeat 2–3 times
4. Refill with 50/50 coolant-distilled water mix

Extra Coolant Tips

• Concentrated vs. Pre-Mixed: Some coolants are sold as full-strength and must be diluted. Others come pre-mixed—always read the label.
• Check for leaks or discoloration regularly. Brown or sludgy coolant means it’s time for a flush.
• Supercharged or performance engines (like on some Mustangs or Cobras) may have separate cooling systems—check each system’s specific requirements.
• Stick with the original coolant type your car came with for best long-term reliability.

Final Thoughts

Coolant isn’t just a maintenance afterthought—it’s essential to keeping your engine running safely and efficiently. Understanding the types, colors, and correct usage of coolant can save you from major engine damage, overheating, and expensive repairs.

Golden rule:
Match the coolant type to your vehicle. When in doubt, stick with the original color and chemistry or consult your manual.

Want a one-size-fits-all backup? Prestone’s universal coolant is a safe bet—but only if you flush first.

Got questions or a weird coolant color in your overflow tank? Drop a comment or message—we’ll help you figure it out.