All about Automotive Cooling Systems

Submitted By: Kit Sullivan, Director of Training
Southern Express Lubes, Inc.

“Wow! That car is hot!” If spoken in regards to your classic muscle-car’s ability to elicit complimentary remarks, you are all set! On the other hand, if by ‘hot’ they are making reference to the growing puddle of anti-freeze that seems to collect on the ground every time you drive your car, that is another story altogether. Does your car seem to run hot at idle, but settles into its ‘normal’ zone once you start driving? If so, there may be a few pointers about the automotive cooling system that can help you alleviate that ‘hot under the collar’ feeling.

THE BASICS!
Even though the mechanics of a typical automotive cooling system are simple enough for even a moderately-knowledgeable person to understand, there are still a few things that can even ‘trip-up’ an expert. Let’s start with the basics of an automotive cooling system. First of all there is the engine block itself. Running throughout the engine block are passages designed to let engine coolant flow to as many areas as possible to cool the engine as it is running. These passageways are known as the ‘water jacket’. Some engine blocks have a very efficiently designed water jacket, which allows an engine to effectively ‘shed’ the heat it generates into the surrounding engine coolant on a consistent basis. Unfortunately, there are also some engine blocks out there that do not have the most well-engineered design when it comes to water jackets. Theses type of engines will be prone to localized hot-spots in the engine, which can lead to premature head-gasket failure, oil leaks, and shortened engine life. An engine’s water jacket cannot be changed or modified in any way, so any improvements must come from one or more of the other components that make up the cooling system.

MOVE THAT COOLANT!
The coolant must be moved throughout the engine, and that duty falls to the water pump. On our classic cruisers, the water pump is most often attached to the front of the engine, and is usually driven by a belt attached to the engine’s pulley-system, although some high-performance aftermarket water pumps can be electrically driven, as are most of today’s modern cars.

WHERE ARE WE MOVING IT TO?
As the water pump causes the coolant to travel through the engine’s water jacket, it picks up at holds heat away from the engine itself. The coolant continues on out of the engine through a hose attached to the upper section of the radiator.

The coolant travels through many tiny tubes from the top of the radiator to the bottom, and these tubes have tiny fins attached to the outside of them. As air flows across the surface area of these fins, the heat that is held in the coolant is released to the outside air, lowering the temperature of the coolant.

BACK TO THE ENGINE!
The now lower-temperature coolant travels through a hose attached from the lower section of the radiator back into the engine to repeat the process all over again! In its most basic form, that is essentially the design and function of a typical cooling system. However, there is much more to consider than that. A typical engine is engineered to run at around an average temperature of 250-260 degrees. Water boils at 212 degrees (at sea level). Water, like any liquid, will absorb, and continue to hold more and more heat until it reaches its boiling, or vaporization point. At the point of vaporization, this boiling liquid will spontaneously release all of its stored heat. This is called the ‘Latent Heat of Vaporization’ law. It is this unbendable law of nature that allows a vehicle’s cooling system to operate. If we were to allow the coolant to boil, or vaporize at 212 degrees, it would do so inside your 250-degree engine, releasing all that heat back into your motor. That’s no good. No, we need to keep it in a liquid state, non-vaporized, so it will continue to hold heat.

PRESSURIZE IT!
At an ambient (surrounding) air-pressure equal to ‘sea-level’, water boils at 212 degrees.
Decreasing the air pressure on any liquid will allow it to boil at an even lower temperature. Likewise, increasing the air pressure on any liquid will raise its vaporization, or boiling point.
For every 1 pound of pressure applied to water above ‘sea-level’, the boiling point of that water is raised by approximately 4 degrees.

So, if you were to increase the pressure on your cooling system’s coolant by 15 pounds (over ambient), you would be adding an additional 60 degrees of temperature holding ability, added to the initial 212 degrees, for a total of 272 degrees before the fluid would vaporize, and release all of its heat.

272 degrees is well above the 250 degree operating temperature of most engines, and this is what allows our cooling systems to operate as effectively as they do. Most vehicles operate with a radiator cap that will apply an additional 15-16 lbs. of pressure over ambient, giving us the ability to keep our engines cool, yet still hear the occasional “Man, that’s hot!”

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