Keeping Your (Car) Cool In The Summer Sun

By Brian Klaubert

Hot days can cause cars to run hotter than usual. You may see your temperature gauge go higher than it has seemed to in the past. How high is okay for the temperature to go? Lets start by understanding the engine cooling system a little better.

Many cars have electric cooling fans. If you hear a fan start and stop when your car is parked but running, you probably have an electric cooling fan. These cars are actually designed to allow the car to run pretty warm. Most electric cooling fan systems have a low mode and a high mode. What is surprising is the temperature setpoints for the fans coming on. Most electric fans are not supposed to turn on in low mode until the coolant temperature reaches 225 degrees. High mode is usually programmed for 235 degrees.

When you turn the air conditioning on, most cars will automatically go to high mode. This masks early symptoms of cooling system problems. Because most of us in Atlanta leave our air conditioners on practically year round, our cooling fans are almost always in high speed mode. Problems with the other normal cooling modes are masked because the air conditioning system is commanding high cooling mode all of the time.

Many of you may remember that water boils at 212 degrees. So why doesn’t the radiator boil over when the normal cooling fan operation allows the temperature to reach 235 degrees? Your radiator cap is the answer. Your radiator cap is actually a pressure valve. It allows the high temperature water to pressurize the radiator up to 16 pounds of pressure.

As radiator caps age, they loose their ability to hold pressure. It is very common to find radiator caps only holding 10-12 pounds of pressure. Some won’t hold any pressure. The lower the pressure that the cap maintains, the more coolant that is pushed from the radiator to the overflow bottle each time your car warms up. Repeated cycles of this can lead to the radiator system being low on fluid. Low fluid level eventually causes a car to overheat.

Another symptom is a gradual degradation in the efficiency of the radiator. The radiator cools sufficiently for cold weather and even warm weather. But when those real dog days hit, the radiator can’t keep up. Most radiators will last 5-7 years. After that they usually begin to succumb to either inadequate cooling or to leaks from corrosion. If your temperature gauge is higher than normal when driving above 60 mph, it is likely that your radiator needs replacement.

So what temperatures are normal? When your car is moving, the temperature should be between 195-215 degrees. When you are sitting at a traffic light there is very little air flow through the radiator. It is normal for the temperature to increase 10-20 degrees from its temperature when moving, but it should not go up more than 20 degrees or over 235 degrees.

But the best rule of thumb is to keep track of where the temperature normally runs. When it gets above that range, have your car checked out. Catching a problem in its earlier stages can prevent being stuck on the side of the road later on.

Brian Klaubert owns Christian Brothers Automotive – Hamilton Mill on Hwy 124 in Dacula, 2004 winners of “Best of Gwinnett” in both the Gwinnett Daily Post and Gwinnett Magazine.