How do I know which antifreeze to put in my car?

[EthanMarie]

Consulting your vehicle's owner's manual is the only definitive way to know which antifreeze or coolant to use. Using an incorrect type can lead to severe engine damage, including corrosion, clogged cooling systems, and overheating, with repair costs often exceeding $1,500. The manual specifies the exact chemical formulation and performance standard required by your engine's manufacturer.

Your owner's manual will not simply list a brand name. Instead, it mandates a coolant meeting a specific OEM (Original Equipment Manufacturer) specification, such as GM Dex-Cool, Ford WSS-M97B57-A, Mercedes-Benz MB 325.0, or BMW LC-18. These codes are based on the coolant's chemical technology. The three primary types are:

• IAT (Inorganic Additive Technology): Traditional green coolant for older vehicles (pre-2000s), requiring replacement every 2-3 years or 30,000 miles.
• OAT (Organic Acid Technology): Common in modern GM, VW, and many Asian vehicles, typically orange, red, or dark green, with a 5-year or 150,000-mile service life.
• HOAT (Hybrid Organic Acid Technology): A hybrid used by Ford, Chrysler, and many European brands, often yellow or turquoise, with a similar 5-year lifespan.

Coolant color is a general indicator but is not a reliable guide for selection. Different manufacturers use the same color for different chemistries. Pouring a red OAT coolant into a system designed for red HOAT can still cause damaging chemical reactions. Always match the specification, not the color.

If you've lost your manual, locate the coolant specification through:

1. Contacting an authorized dealer with your VIN.
2. Checking reputable online automotive databases.
3. Looking for a label under the hood that states the required fluid specification.

For topping off, use a pre-diluted 50/50 mix of the correct coolant type. For a full flush, you can use concentrated coolant mixed with distilled water. Never mix different coolant technologies. If you are unsure of the existing coolant, a complete system flush with the correct new coolant is the safest procedure.

Coolant Type	Common Colors	Typical Service Life	Key Vehicle Applications (Examples)	Primary Risk of Mismatch
IAT	Bright Green	2-3 years / 30k mi	Older domestic & Asian cars	Rapid corrosion, silicate dropout
OAT	Orange, Red, Dark Green	5 yrs / 150k mi	GM, VW, Hyundai, Kia	Gel formation, heater core clog
HOAT	Yellow, Turquoise, Pink	5 yrs / 150k mi	Ford, Chrysler, BMW, Mercedes	Additive dropout, reduced protection

[McEvangeline]

I learned this the hard way. My old sedan overheated, and the mechanic showed me a sludgy, gel-like mess in the radiator. I’d topped it off with a “universal” coolant that was the wrong type. The repair bill was over $1,200. Now, I keep a photo of the coolant spec page from my owner’s manual on my phone. Before I buy anything, I cross-check that code on the bottle’s “meets specification” list. It takes 30 seconds and saves a fortune. The color in your overflow tank means nothing—the factory code is everything.

[OliviaMarie]

Forget the color. As a technician, I see cars every week where someone guessed based on the pink or green fluid they saw. Modern engines have specific materials—different aluminum alloys, solder, seals. The coolant is formulated to protect those. The right spec prevents corrosion of the water pump and aluminum heads. When you mix types, the inhibitors can neutralize each other, leaving the system unprotected. If you’re topping off a near-empty reservoir, use distilled water to get to a shop and have them check it properly. For a flush, insist on the OEM-specified coolant, not just what’s on the parts store shelf. Your engine’s longevity depends on it.

[DelCassandra]

Here’s my DIY process. First, I open the glovebox and find the manual. I look up “coolant” or “capacities.” It gives me a code like “Ford WSS-M97B57-A.” I go to the auto parts store and ignore the big color banners. I pick up bottles and read the fine print on the back until I find one that lists my exact code. I always buy the 50/50 pre-mix for top-offs—it’s foolproof. If the system is dirty or I’m changing it, I do a complete flush with distilled water before adding the new, correct coolant. Keeping a spare bottle with the right spec in my garage means I’m never tempted to use the wrong thing in a pinch.

[AliceLynn]

My perspective comes from owning a European performance car. The cooling system is complex, with an intercooler and specific heat transfer demands. The manufacturer’s specified coolant, often sold at the dealership, is formulated for a reason. While aftermarket “compatible” options exist, the price difference is minimal compared to the risk. Using the exact fluid ensures optimal performance and preserves warranty claims. I follow the factory service interval strictly—for my car, that’s every four years. I document the service with the coolant specification listed on the receipt. For high-strung or luxury engines, this isn’t an area for compromise or experimentation.