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 solid 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 by transferring heat from the engine to the radiator.
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.

The most common glycol used in antifreeze is ethylene glycol, a toxic material that can cause death if ingested, and requires very specific handling. Spills of ethylene glycol-based coolant should be washed away so cats and dogs do not ingest it. Never leave used coolant around to evaporate; it doesn?t. Always store used coolant in bottles with child-proof caps so children can?t easily drink it. Never store coolant in juice or punch bottles that might make their way into the kitchen. Ethylene glycol-based antifreeze usually contains a bittering agent to deter human ingestion but this does not stop pets from drinking it. Antifreeze will biodegrade in a few hours on a warm day and can be returned to Valvoline Instant Oil change or similar locations for recycling if used coolant is not sewerable in your area.

An alternative antifreeze base is propylene glycol, but it costs more than EG and does not provide as much freeze protection nor heat transfer capability. There is very little difference in the corrosion inhibitor additive performance of either substance. Propylene glycol is slightly less toxic than ethylene glycol. Propylene glycol is slower to biodegrade than ethylene glycol and is more flammable. Always handle coolants with great care and dispose of them properly.
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 are system pressure caps, rather than simple plug or twist-off caps.

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. If the top radiator tube is hard, the system is pressurized. Do not open it. The system should be pressurized if it is hot and the radiator cap is working. When the top hose is easily squeezed, 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 clear. Long-life coolants are yellow, red, purple and orange. Vehicle manufacturers employ very different 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.
Next, if the system is full and the fluid looks clear, check the freeze point. This will tell you if the coolant to water mix is correct and confirm that the fluid will protect the engine. There are many types of freeze point testers. The best types are based on refractive index and are used by mechanics. The floating ball or swinging arm types work on density differences and look like turkey basters, in a wide variety of shapes and sizes. These devices are inexpensive and made of plastic in places like China, usually.

Always check them with pure water, and a 50/50 mixture as a control and convince yourself the darn thing is working. If they have been dropped, they can break and read incorrectly. Also the cheap plastic construction can absorb glycol and not respond correctly. Make sure the coolant is cool when you do this or it may melt your tester. If you find the tested is non functional, take it back to the store where you bought it and exchange it. These jewels can be bad right out of the box; always calibrate them.

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.


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