Antifreeze: Red, Green, or Universal? That is the Question!

Classic Car Radiator
Giant Classic Car Radiator. Photo by Mark Gittelman

Used to be, every make and model of car required a specific kind of coolant (sometimes called antifreeze). These days, however, there are universal coolants on the market that provide a broad spectrum of protection.

What's in a Color?

Decades ago, the color of specific coolants related directed to the chemicals they used to prevent corrosion. Red, pink, green, blue, orange, yellow—it all got so confusing. Fortunately, individual manufacturers now spell out their coolant specifications in the owner's manual or on a decal on the coolant reservoir. Just match those specifications with the coolant at the auto supply store, and you're good to go.

Universal Liquid

Most conventional green or blue coolants use an inorganic (IAT) technology to prevent corrosion, that is, they are ethylene glycol or propylene glycol based. But what about universal coolants, or those formulations that claim to be good for any year, make, and model of car?

Several factors make them universal, most notably organic-acid technology (OAT), a uniquely concentrated single-component, multi-metal corrosion inhibitor. These contain proprietary organic acids, including carboxylate, to provide broad-spectrum protection. Many mechanics and car club members have used this newer technology without incident. 

However, you should follow these steps when using:

  1. Completely flush out the old coolant.
  2. Make a commitment to continue the normal three-year/30,000 mile scheduled maintenance.
  3. Remember to periodically test the coolant's pH level with a dip strip.
  4. Finally, if you live in a cold climate, make sure you test the freezing point.

Breaking the Old Antifreeze Habit

There are advantages to using only one type of coolant, both for newer and for classic cars. Classic car owners traditionally use inorganic acid coolants, the ones that are ethylene-glycol-based and bright green in color. If you own a 1976 Cadillac Coupe Deville or a 1957 Chevrolet Nomad two-door station wagon, for instance, this is the type of fluid you'll see.

But using an OAT-based universal coolant will be fine in your classic car. That way, you don't have to surf the internet or thumb through old owners' manuals (assuming you have them) to try and figure out which antifreeze/coolant to buy for your make and model.

Do keep in mind, though, that maintenance intervals will remain the same, generally every three years or 30,000 miles. It's important to follow these maintenance guidelines as the PH level of the antifreeze can change over time and become acidic. Regular fluid changes can prevent damage to the cooling system's most vulnerable component, the radiator.

Keep the Extended Life Antifreeze in Newer Cars

What about extended-life antifreeze? Our advice is this: Just because the universal-style coolant works great in the classics doesn't mean we recommend draining the extended-life coolants from your newer vehicles. 

These extended life coolants (most of which are also OAT-based) can extend service up to 10 years/100,000 miles, instead of the three years/30,000 miles that are typical with the old green stuff. With this kind of protection, it would seem wasteful to drain it out prior to its recommended service interval. At any rate, extended-life antifreeze isn't recommended for your classic car because it can eat away at older-style radiators that have lead-based solder.