Some common sense: Never open a hot radiator capWritten by Nick Shultz | | email@example.com
Hidden underneath all the computer controls of a modern vehicle is something surprising. If you strip away all wiring, the sensors, the actuators and other computer-related devices you will find something very functional. Underneath it all is an internal combustion engine. The engines in today’s vehicles operate almost identical to the ones that Henry Ford put into the Model “T.” They may look a lot different. They may sound different. Nonetheless, they are nearly identical in operation.
Today’s high tech engines and yesterday’s old-school engines use the laws of physics in order to work. We might be able to break the laws of men; however, we cannot break the laws of physics. Understanding those laws and how they apply to the operation of the internal combustion engine is required to properly diagnose them.
Two, of the many physical laws that govern the operation of the internal combustion engine are the laws affecting pressure and temperature. Those physical laws require that an area of high pressure will always move (flow) to an area of low pressure. Never the opposite! High temperature will always flow (move) toward an area of low temperature. Again, never the opposite! The greater the difference between two pressures, or two temperatures, the faster the movement between the two will be. This is valuable information for the auto enthusiast. It explains how an engine breaths and cools. It also explains a lot about how life works, as well!
A great example of these laws, working in everyday life, is in our own homes. When we open the door on a cold winter’s day, we feel the effects of the physical laws governing the movement of heat. The heat from within the house rushes towards the outside cooler air. Again, hot always moves to cold. The same is true for our bodies. When we are outside in the middle of winter, the heat from our bodies tries to escape to the colder atmosphere around us. The secret to staying warm, therefore, is not letting the heat escape. Another good example is when we boil water on the stove. When you remove the heavy lid of a pot of water you may see that it immediately begins to boil. That’s because the laws of physics are at work.
I thought it would be good to share this knowledge with you so that you may better understand what went wrong when a gentleman from New Jersey was trying to fix his car along the freeway.
This past weekend I was driving north along U.S. Route 23 when I came upon a man standing beside his Toyota SUV with the vehicle’s hood up. I pulled over to see if I could help him. He had his hands wrapped with a towel and it was obvious that he was in pain. He said that he had opened his radiator cap in an effort to add coolant to his overheated engine. As soon as I released the cap, he said, it blew off and boiling water came out of the radiator and burned me. One look at his hands and I knew he would need medical attention. The overheated engine would have to wait.
This New Jersey man made one serious mistake; he opened his radiator cap when the coolant was hot. It is written directly on the radiator cap, “Never Open Hot.” Yet, far too often, folks will open the cap when the liquid inside is hot and under pressure. The result can cause serious burns. There is some Physics at work here we should be aware of. Water has a higher boiling point when it is under pressure. Water normally boils at 212 degrees Fahrenheit at sea level. The Toledo area is around 650 feet above sea level, depending upon where you live. When we add pressure to water we raise its boiling point. For every pound of pressure that is applied to water the boiling point is raised by 3 degrees Fahrenheit. Most vehicles today come with a 15 pound radiator cap. That means that 15 pounds of additional pressure develops within our coolant systems. This additional pressure raises the boiling point of the coolant inside by 45 degrees, resulting in a boiling point within the coolant system of 257 degrees Fahrenheit. The actual temperature inside the coolant system is regulated by the coolant fan which generally is activated at about 220 degrees Fahrenheit. This means that the temperature within the radiator is well above the normal boiling point of water. The actual temperature the coolant fan comes on varies slightly from vehicle to vehicle. It is obvious that the temperature in a normally operating coolant system is well above the normal boiling point of water when it is exposed to atmospheric pressure.
This is exactly what happened to the New Jersey man. Once he opened his radiator cap, the hot coolant inside came boiling out under pressure. The boiling liquid burned his arms and hands.
My advice is to let the vehicle cool before opening the cap. When dealing with the coolant system, patience is not just a virtue, it is mandatory. I also advise that you not add cold water to a hot engine. Another couple of physical laws apply when you do that and the result is almost always bad. If you follow these common sense steps you will begin to develop your auto sense.
Nick Shultz is an instructor of Automotive Technologies at Owens Community College. He is a certified Master Automotive Technician.