The Importance of Coolant

Another easy way to protect your engine

Whether you call it engine coolant or antifreeze, the fluid in your radiator multi-tasks, circulating throughout your engine block and keeping the works purring like a kitten.

What is Coolant?

Generally, coolant is a half-and-half mixture of a form of glycol and water. The glycol represents the antifreeze element of the mix, guaranteeing that the fluid doesn't turn into ice under harsh winter conditions. On the other hand, glycol also prevents the coolant from reaching the boiling point in Death Valley heat; it keeps engine temperatures stable under all climate extremes and driving conditions.

Interestingly, pure water actually transfers heat better than coolant (that's why you see straight water used in the radiators of some types of racecars). However, coolant/antifreeze includes additional additives that prevent rust and corrosion in the radiator, engine and the vehicle's heater.

Until recently, the most common glycol in antifreeze was ethylene glycol, a toxic material that can cause birth defects, reproductive damage or even death if ingested, and requires very specific handling. Ethylene glycol has a sweet odor and flavor, which makes it dangerously appealing to animals and/or small children.

An alternative antifreeze base is propylene glycol. There is very little difference in the performance of either substance; the advantage is the toxicity level. Propylene glycol is significantly less toxic than ethylene glycol. This doesn't mean children or pets can ingest it without harm, but, like alcohol, propylene glycol is not toxic at low levels.

Any antifreeze, whether ethylene or propylene glycol based, picks up heavy-metal contamination during use. For this reason, special care must be taken to dispose of used antifreeze. It's safer to have a repair facility flush your cooling system since they are required by law to dispose of the material safely.

Most communities have procedures for disposing of hazardous waste; so, if you do your own repairs and maintenance, take advantage of these procedures. Don't pour coolant down your sink or into storm drains.


Like any other engine fluid, the coolant needs to be checked on a regular basis. You're checking for two things: quantity and condition. Since the 1970s, most vehicles have a coolant recovery tank or overflow reservoir, which makes checking the fluid level a lot easier and safer. The configuration of the radiator and tank/reservoir lets hot coolant expand into the tank as the engine temperature rises. When the engine cools down, a slight vacuum forms in the radiator and the fluid is drawn out of the tank/reservoir and back into the radiator. As long as the radiator cap remains sealed, the coolant can expand and contract without losing a drop.

You can check your coolant level simply by looking at this overflow tank. There are two level indicators on the side of the tank: one indicates the safe level when the engine is hot, the other when cold. If your coolant level is slightly low, it's safe to add a few ounces of plain water to bring the level back up to the appropriate mark. If you have to add more than a quart of liquid to the cooling system, use a glycol/water antifreeze mixture.

Nothing is ever all that simple, though. Some vehicles' recovery tanks are pressurized when the engine is hot, making the caps as dangerous to remove as radiator caps. Pressurized recovery tanks are clearly marked with warning decals and their caps is a system pressure cap, rather than a simple plug or twist-off cap.

Adding Antifreeze

If the recovery tank is completely empty, you'll need to add a mixture of antifreeze/water to the radiator. Make sure your vehicle has had at least 30 minutes, and preferably longer, to cool off, so that the radiator hose is not hot to the touch. Remove the radiator cap, checking to make sure the cap's rubber seal is in good shape, and add the mixture to the top of the radiator neck. Put the radiator cap back on securely, and add the coolant to the cold level in the recovery tank.

In addition to checking for an adequate amount of fluid, you should examine the condition of the fluid. Coolant that's still working looks like clear, slightly thick lemonade, a pale greenish-yellow color. Long-life coolants are orange, like pale orangeade. Some vehicle manufacturers employ a beige-colored fluid. No matter what the color, the key is that it's not brownish or dirty looking and that flecks of rust aren't floating around in it.

If the coolant is in bad condition, it's time to have the system flushed. The most common service interval for flushing the system is every two to three years, or 24,000 to 36,000 miles. When your vehicle goes longer than that timeframe without fresh fluid, you're engine may suffer some damage. So take care of your coolant-and your engine will keep its cool.

Afraid of paying too much?
Get price quotes from dealers
near you... get ready to SAVE!

Get Internet Price