Years ago, car radiators only had water in them, but these days, a radiator has a 50/50 mix of a glycol-based antifreeze/coolant and water. You don’t have to mix it yourself; the kind you buy in any auto parts store – or the kind your mechanic uses – will come pre-mixed.

Out of necessity or preference, sometimes you may need to add water to your radiator. You don’t need to use bottled water. Any clean water will do, even tap water, but distilled water will introduce fewer impurities into your radiator. If you’ve got a choice, distilled water is the way to go.

Most experts suggest using a 50/50 mix of antifreeze and water in your radiator. That’s why most commercial antifreeze you buy in an auto parts store already comes pre-mixed into the ideal ratio.

Why is it important not to run straight antifreeze (ethylene glycol)? It might seem counterintuitive but pure antifreeze actually has about 35-percent less capability to transfer heat than pure antifreeze. That means you’d be defeating the purpose of coolant because your engine would overheat at a lower temperature and freeze up at a higher temperature.

Plus, pure antifreeze is more corrosive to your radiator than the 50/50 recommended blend, potentially setting you up for leaks or other issues in the long run.

First off – and this is really important – don’t try to test a hot engine. Perform any and all tests when the engine is cool and no longer running.

There are 4 main ways to check your coolant:

• Visual test: Does the coolant look the right color? When you remove the radiator cap, do you see sludge? If the coolant is brown, that indicates rust and corrosion. If you normally have green antifreeze, it’s easier to see if it’s brown. If you normally have orange or red antifreeze, it’s tougher to tell but if it looks cloudy or muddy, you need to change it.
• Hydrometer: Uses a handheld tool that you can probably buy at your local auto parts store to test the specific gravity of your coolant. It’ll show the temperatures (high and low) that the radiator fluid is still protecting at.
• Multimeter test: Uses a low electric current to see if there’s a charge in your coolant. (Be careful with this one whenever there’s electricity involved)
• pH test: You can buy a specific test for this or use small test strips that may also test the pH of a fish tank, hot tub or pool. Dip the test strip into the coolant when the engine is cool. You want the pH to be between 8.5 and 10. Anything outside that range and you should consider changing the coolant.

But, of course, for most people, it just makes sense to leave this to the professionals at your local service center. This could be one of those questions where, if you’re asking how to do it, maybe the job isn’t for you.

Pretty much the answer is Yes. The words antifreeze and coolant are essentially interchangeable. Each term represents one property that the fluid has, but no matter what you call it, antifreeze/coolant protects your engine from extreme temperatures.

• Coolant: Your engine generates an incredible amount of heat, the coolant keeps the engine cooler and still operating at temperatures above the boiling point of water.
• Antifreeze: In winter (and in other times too), temperatures drop below freezing in most parts of the country. If it were just water, the fluid in your radiator would freeze, and the fluid would expand and hurt the engine. Instead, antifreeze will protect your engine down to -34 degrees Fahrenheit.

Your Owner’s Manual can tell you what the maintenance interval might be for your specific car, but if you have conventional coolant, your first coolant flush might happen at 45,000 miles and then every 2 years and 30,000 miles after that.

Newer cars, especially import cars, often have more advanced antifreeze that’s meant to last longer. Check with the experts at your local auto service center, but you might be able to go 5 years and 100,000 miles or longer.