Wheels: Coolant and antifreeze

By Eric Meltzer
What's the difference between coolant and antifreeze? In short, nothing, but in places like New England where liquid tends to freeze in winter many people refer to that colorful liquid as antifreeze. However, the primary purpose of this fluid is to act as a coolant for your engine, even in the dead of winter. We've discussed the inner workings of an engine in past columns but one prominent by-product of an operating internal combustion engine is heat. This is a good thing especially on those cold winter days. It's also a bad thing if left unregulated. The cooling system of your car, like many systems in your car, is more involved than one might think. Your engine is cooled via heat transfer. That is, the heat in your engine is transferred to the coolant which circulates throughout your engine and eventually dissipates into the air. Let's follow the coolant as it travels around your engine; this is a simplified, typical model and your vehicle may differ slightly.
Starting at the overflow bottle, the point at which you add coolant if necessary, this reservoir feeds the radiator. Through the lower radiator hose, the coolant is propelled by the water pump through small water jackets in the engine which thread their way around the cylinders and cylinder heads. As the coolant moves around the engine it's effectively absorbing the heat which is good, especially in winter, because the next component on our journey is the heater core; essentially a mini radiator with fins to increase surface area and radiate the heat to your car's interior with the help of the blower fan. Turn the heat up in your car and you're opening a small valve allowing more hot coolant into the heater core. The small tubes in the heater core can also pose problems which we will go into later. After circulating through the heater core the coolant moves back through the engine and passes the thermostat. This thermostat is a small disk that stays closed under spring pressure and limits flow until the engine warms to operating temperature. Once the preset temperature is reached, the thermostat opens allowing the coolant to complete it's journey back to the top of the radiator. The hot coolant is then cooled as it passes down through the radiator by air passing through it as you drive. It is helped by the engine fan which draws air through the radiator more rapidly and when additional cooling is needed. The whole system is sealed and pressurized and works quite effectively.
Pure water is actually a good coolant and in the early days of motoring, that's exactly what was used. Freezing was a problem then too so wood alcohol or methyl alcohol was used but it was corrosive and evaporated quickly. This led to ethylene glycol as it's replacement. That fluid stuck around and modern antifreeze is still mostly glycol, either ethylene or propylene; the main difference being that propylene is less toxic than ethylene although care should still be taken regarding spills and storage especially when kids and animals are around. The glycol provides the freeze protection and the rest of the coolant is made up of additives. Water is still an important component of coolant and optimum protection is achieved when you dilute straight coolant with a blend of 50 percent coolant with 50 percent water. This allows freeze protection down to minus 34 degrees Fahrenheit and boil-over protection up to 265 degrees Fahrenheit. But be aware that some modern coolants are packaged as pre-diluted or more commonly, ready to use. Further dilution of these will degrade their performance. Similarly, too little water is equally detrimental and will not allow the maximum cooling and antifreeze properties to be reached. A minimum of 30 percent water should be used as a dilution ratio with 50 percent water as optimal. Water contains hardness and chlorides which contribute to scale and deposits. For these reasons distilled water is preferred for dilution but common water is acceptable.
In simpler times coolant was green, automatic transmission fluid was red, oil was brown and you could identify a leak simply by looking at the drip or puddle under the car. How times have changed! Coolant now comes in a rainbow of colors and it's important to use the correct one. The difference is partly in the base glycol component but the majority of the difference is in the additive package. Corrosion inhibitor additives have changed to work with newer aluminum alloy engine materials as well as other advanced alloys now used in engine design and construction. However, the most important fact is that the different coolants are not compatible. When mixed together they react chemically and all kinds of bad things can happen from forming a gel-like substance to accelerating corrosion to something as minor as shortening the coolants effective life. Remember those small tubes I mentioned in your heater core? Those are the first to clog when the coolant gels. If your engine is running at operating temperature but your heat is weak it's probably time for a flush with an appropriate solution to dissolve any gel, scale, corrosion, and deposits; simply flushing with water won't be effective for long if at all. We see this in our shop a lot. If your car is taking longer to reach operating temperature than it should, suspect the thermostat. This is not uncommon and is another component easily affected by buildup in the cooling system. If your engine is running hot and the temperature is building but you have no heat you probably have no or low coolant; stop and check the level. There are "global" coolants on the market designed to mix with any other coolant but my recommendation is to stick with the correct fluid whenever possible. That's not to say run your car low or without coolant, anything is better than nothing, but the correct coolant is always preferred.
Flushing the cooling system is a regular maintenance item and should be done to maintain the cooling system at peak efficiency. The freeze and boil over protection of glycol is permanent but those additives get used up. Regular green coolant is good for three years or 30,000 miles while the new long life coolants should last for five years or 100,000 miles. Remember, the concern is corrosion protection and lubricity; just testing the freeze point is not enough to ensure the coolant is good.
Regardless of the type of coolant, they all have a sweet smell. The cooling system is a sealed system so anytime you smell coolant something is wrong, get it checked out even if you don't see a puddle or obvious leak. Cooling systems operate under pressure and at high temperatures. Heed all warnings and never open a hot cooling system. Many water pumps are belt driven; driving a car with an inoperative water pump is a recipe for disaster. Similarly, operating a cooling system with no or inadequate volume of coolant is just as damaging. An overheating engine commonly leads to warping components and major engine work. If your car is running dangerously hot for any reason, stop immediately and let it cool. I assure you the towing bill will be much less than the bill for the engine work.

Eric Meltzer owns and operates Fryeburg Motors, a licensed, full-service automotive sales and service facility at 299 Main Street in Fryeburg, Maine with his wife, Michelle, and lead technician, Craig. Eric has always been into cars and appreciates anything that drives, rides, floats, and flies.