- Thu, Mar 1, 2007
Mid-Winter Greetings from Snow Covered Nappanee….
Here's hoping this writing finds you all comfortably settled in for the winter, with a slight twinge of excitement in anticipation of the warm spring weather ahead. I know spring can't come soon enough for me.
In this time of Winter cold, we are going to take a little while to talk about heat… maybe that will help warm us up a bit… but not the heat from your furnace. This month we are going to talk about the cooling system in your car, RV, or tow vehicle. As different as they are in size from one vehicle to another, they all have exactly the same task in life; to maintain the engine temperature in a specific, carefully designed temperature range.
There you are, cruising down the highway on vacation... not a care in the world, making good time as you travel toward your destination, when suddenly the hair on the back of your neck stands up. The unmistakable smell of antifreeze permeates the air, and before you know it, warning lights are on and you are sitting by the side of the road with steam spewing from under the hood. How in the world could this happen?? Not now, not to you, and not on your vacation! To understand how we got here, let's look at the typical vehicle cooling system.
Vehicle engines use chemical energy (burning fuel) to create mechanical energy (pushing pistons). This process creates heat; often enormous amounts of heat. To counter that heat, the cooling system has to absorb, take away, and dissipate the heat that is being generated. Not an easy task, given that some areas of the engine that are subjected to combustion temperatures of between 2000 and 3000 degrees. While some of the heat is used and necessary for the internal combustion process, about one third of this heat is wasted heat. Studies have shown that a 3.0 liter V6 engine pushing a 3800 lb. car down the road at 60 mph generates enough waste heat to comfortably heat a 3 bedroom house in the dead of winter.
Since most engines are designed to run in the 190 - 215 degree range, maintaining this critical temperature falls on the cooling system. The typical engine cooling system consists of a radiator (with a special cap), water pump, heater core, thermostat, coolant, and a variety of hoses used to circulate the coolant during the cooling process. Let's look at how the system works and each of these components, and their function in the system.
First, the engine generates the heat. As the engine temperature rises, a thermostat opens at a set temperature, allowing coolant to begin to circulate through the system. From the engine block, the coolant is pushed by a water pump through the thermostat and out into the radiator via the upper radiator hose. The "radiator" uses air flowing through its coils to create thermal convection to dissipate the heat the coolant is carrying. Once cooled, the coolant returns to the engine block via the lower radiator hose, where it is again circulated through a maze of tunnels and pockets (called "Water Jackets") in the engine block and cylinder head(s) to absorb more heat. Most cooling systems also use a set of smaller hoses to pass the heated coolant through the radiator core to warm the interior of the vehicle. Simple enough, right? But what exactly does each of those components do?
Since water has a tremendous capacity to carry away heat, it is a logical choice to perform that function. For every degree in temperature rise, water can absorb ten times as much heat as cast iron, or five times more than aluminum. Ethyl Glycol, the main ingredient in automotive anti freeze, has a 25% lower heat capacity than water, so you never want to run straight "antifreeze" in your car as it will cause overheating in hot weather. When mixed with water, however, antifreeze raises the boiling point of water, so a 50/50 mixture with water is just about ideal to handle most loads the cooling system would fall under.
A 50/50 mixture of water and anti freeze will boil (with the radiator cap open) at approximately 225 degrees (f). However, with the radiator cap in place and the system sealed, the boiling point rises about 3 degrees for every pound of pressure the system builds. A 15 psi radiator cap will put the boiling point around 265 degrees.
Speaking of the radiator and its cap, these are the critical parts of the cooling system that are often the most neglected. In order for the engine to maintain that critical temperature range that is ideal for, a certain amount of thermal convection must take place in the radiator. There are three things that often prevent this from happening. One is a partially plugged radiator. Internally, accumulated deposits can plug all or a portion of the radiator, reducing it's coolant flow, and subsequently it's ability to dissipate the heat the engine is generating. Second, the coils can, over time, become plugged with insects, road grime, and impacts with foreign objects (rocks, tire rubber, road debris, etc.). Finally, a defective radiator cap can limit cooling by opening too early, not allowing the system to build pressure properly, and allowing coolant to escape from the system. Though not part of the radiator, a failed cooling fan will also cause an overheating condition as it will not draw sufficient air through the radiator for cooling.
The "water pump" is a simple enough device, but its function is imperative to the life of the engine. The "water pump" circulates the coolant through the cooling system via it's impeller. Because this is a moving part, it is subject to wear, and should be inspected periodically. Any seepage of coolant, or play in the shaft that drives the impeller is an indication of a failing water pump, and it should be replaced immediately.
The thermostat job is to block the flow of coolant so the engine will warm up quickly, then to maintain the engines operating temperature within a specified range. Most are set somewhere in the 190 - 195 degree range. Testing a thermostat is as easy as boiling water. Place the thermostat in a pan of water on the stove and heat it to the point of boiling. Place a thermometer in the water, and monitor the temperature at which thermostat opens. If the thermostat should fail, always be sure to replace it with one of equal temperature settings. Replacing a thermostat with a cooler running one in an attempt to address a cooling problem can cause poor fuel mileage and oil consumption, as well as excessive ring wear. Most engines with electronic controls use engine temperature to signal engine functions, and will not operate properly if the engine never reaches normal operating temperatures.
Other components in the cooling system are the heater core and its associated valve and hoses. While connected to the system, they are not designed to be used in the cooling process. Rather, as you raise the temperature on your vehicles HVAC system, the heater control valve opens and closes to allow coolant to pass through the heater core. The heater core is essentially a small radiator located in the HVAC ductwork in your vehicle. While it's function is similar to that of the radiator, it's size and flow is such that it really does not add significantly to the cooling systems ability to cool the engine.
This month we've looked at the components and function of your cooling system and their importance to the life of your engine. Next month we will take a look at how we can best maintain the cooling system to help insure it doesn't leave you stranded on the side of the road some where.
Until then, may your travels be safe, and if you have a little difficulty along the way, try not to get "steamed"…
See you next month!