A driving looking at his car's coolant reservoir tank.

When to Change Coolant? Before It Ruins Your Engine!

Regular maintenance is key to engine performance, efficiency, reliability and longevity. Knowing when to change coolant, engine oil, transmission fluid and brake fluid, among other adjustments, will help you get the most out of your vehicle.

Looking under the hood, though, it can be difficult to tell when to change coolant. Engine coolant isn’t always easy to judge by appearances alone. If you’re wondering, “Why do you need engine coolant, as opposed to water? What is engine coolant made of? How do you know when coolant is worn out?” don’t worry, because we’ll answer all of those questions and more.

Even in the most efficient internal combustion engines, little of the explosive energy of the fuel is converted to motive power to get you down the road. The rest of the fuel’s chemical energy is lost as heat. Some heat is good, as it improves fuel vaporization and efficiency. Too much heat leads to destructive detonation, engine oil breakdown and lubrication failure. Engine coolant’s sole purpose is heat transfer, balancing overall engine temperature and removing excess through the radiator. Similarly, coolant in hybrids and electric vehicles improves battery life and manages electric motor-generator temperatures.

The Stuff of Engine Coolant

Water is no substitute for a proper engine coolant.Nearly all engine coolants are based on water, an excellent heat transfer medium. Ethylene glycol or propylene glycol make up much of the rest of the mixture, preventing freezing, but you can’t just dump water into your engine if you live in an area that never gets cold. Additives give engine coolant a much longer life than plain water. Corrosion inhibitors, lubricants, anti-foaming agents, colorants and other additives keep the water/alcohol blend from eating your engine.

Additive life essentially determines engine coolant lifespan in any given engine, whatever or wherever you drive. Exposure to heat and oxygen breaks down the additives, leading to the formation of deposits and allowing corrosion to damage your engine from the inside out.

When to Change Coolant

Conventional “green” coolants are usually replaced every few years, while modern “long-life” and “super-long-life” coolants sometimes aren’t even on the regularly scheduled maintenance list. The difference is in the additive package. Green coolant contains inorganic oxides, like silicates, phosphates and borates, which form a protective layer. Long-life coolants are formulated using carboxylates, which react chemically with engine surfaces to prevent corrosion. Formulated to be less polluting, they happen to last far longer.

One way to ensure your engine is well-protected is to change the coolant according to the schedule. However, that could be misleading, causing you to change too soon or too late. A quick coolant checkup, using an antifreeze tester, on a regular basis can tell you if your engine coolant is depleted of additives. Color isn’t a great indicator of coolant condition, but if you see stuff floating in it, it’s ready for a change. If your engine is running hot, even if the coolant level is good, it could mean the fluid has deteriorated. Finally, when you decide to change engine coolant, don’t shop for a certain color, but the type your engine requires.

Check out all the chemical & lubricant products available on NAPA Online or trust one of our 16,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on when to change your car’s coolant, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Ellsworth Air Force Base.

about author

Benjamin Jerew

Ben has been taking things apart since he was 5, and putting them back together again since he was 8. After dabbling in DIY repairs at home and on the farm, he found his calling in the CGCC Automobile Repair program. After he held his ASE CMAT for 10 years, Ben decided he needed a change. Now, he writes on automotive topics across the web and around the world, including new automotive technology, transportation legislation, emissions, fuel economy and auto repair.

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