Every car on the grid is making more power than it did when it was new. At least you hope your car is. When you create more power not all of that increased energy if going to go to the ground. As fuel is burned in your engine only about one-third of the energy in the fuel is converted into mechanical energy. Another third goes out the exhaust pipe and the remaining third becomes thermal energy and is dispersed to the atmosphere through the radiator.
Let’s go back to our high school physics class for a minute. You cannot destroy energy. You can only convert energy. When the air and fuel in your combustion chamber burns it creates thermal energy. Some of that energy is converted into mechanical energy by pushing the piston down into its bore. Some of it is released into the cooling system.
The cooling system consists of the engine's water jacket, a thermostat, a water pump, a radiator and radiator cap, a cooling fan, hoses and usually an expansion tank. Can your cooling system handle the extra demands that you’re placing on it?
What’s a Good Temperature?
Most of us worry too much about our temperatures. In discussions with several engine builders and radiator manufactures there was agreement that it’s best to run in the 210 to 220 range. Even 240 is not a problem under the right conditions.
We all know that water boils at 212 degrees so how do we get above that boiling point? First we pressurize the system. We do this with the radiator cap. Every radiator cap has a pressure rating. Each pound of pressure in the cooling system raises the boiling point by 2 to 3 degrees. If you have a radiator cap that allows for 15 lbs. for pressure your coolant won’t boil until it reaches 250 F. If you use a cap rated at 20 psi you raise the boiling point of the coolant to over 270.
Now let’s put some anti-freeze into the system. The boiling point of ethylene glycol is about 387 F. If you run a 30 % mixture of water and ethylene glycol in your car the boiling point of your coolant would be 220. That’s without pressuring the system. If you have a 20-lb radiator cap there’s only a very small possibility of actually boiling the coolant in your system.
Pure antifreeze though has a higher viscosity rating than plain distilled water. As you increase the antifreeze percentage in your cooling system the ability to adsorb heat from the engine goes down. A higher percentage of antifreeze retards the radiator's ability to get rid of the coolant heat. This is a case of where less is actually better. You should probably never use over thirty percent anti freeze in your racecar’s cooling system.
The Liquid
You always want to start with distilled water. Don’t even think about anything else. This is especially critical if you have an aluminum radiator. A lot of us have racecars with custom radiators. The radiator for a Lola F5000 is not going to be cheap. Why risk the expense of a new radiator by using tap water in that radiator?
We can also add some things to this distilled water. We can start by adding a surfactant. This is a compound that lowers the surface tension of a liquid. It lowers the interfacial tension between a liquid and a solid. What actually happens is a surfactant allows for a greater surface area of the water to come into contact with the radiator tube.
Most anti-freeze has some surfactant. Water Wetter is really just concentrated surfactant. Below 40 is based on the same concept. The idea is that by changing the surface tension of the water you will change the thermodynamic flow from the water to the radiator tube. The surfactant actually allows more of the water molecule’s surface to come into contact with the tubing in the radiator. It changes the water molecule from a sphere to an oval shape.
Ductwork is Critical
The whole cooling system is based on air flowing through the radiator. The more air you can push through the radiator the lower the coolant temperature. Remember the radiator is all about the transfer of thermal energy. More air passing through the radiator means you have greater thermal transfer.
Take a good look at the area between the front of the grille opening and the radiator. Can the air go anyplace other than the radiator? Air isn’t stupid. It will find the path of least resistance. If it can go around your radiator it will.
A fan is only necessary when you’re in the paddock. The only purpose of a fan is to move air through the radiator while the car is stationary. You really don’t need a fan once you’re on the track. A fan uses very little power and it might well be necessary if you do any engine tuning or diagnosis while the car is stationary.
Why Use Aluminum Radiators?
The “tube to fin” contact area determines the radiator efficiency. The secret to better cooling is wider tubes. A typical copper radiator uses 3/8” wide tubes while the aluminum radiators use tubes from 1” to 1 1/4” wide. When a radiator is designed with wide tubes, the tubing wall thickness must be increased to prevent the tube from expanding or a term known as “ballooning”.
Designing a brass/copper radiator with wide tubes is simply not practical because the radiators could very well end up weighing over sixty pounds. Aluminum can be designed with a heavier wall thickness that has very little effect on weight. If your car was originally equipped with an aluminum radiator, then it must stay that way to function properly. If the original factory radiator was brass and copper then you might want to consider upgrading to aluminum.
Use Your Infrared Scan Gun
One very quick way to test the operation of your radiator is to check the temperature of the water going in and the temperature going out. The infrared scan guns are just great for this. You should have very hot coolant going into the top (or side) of your radiator. You should have a significantly lower temperature at the point where the coolant exits the radiator.
The folks at DeWitt radiator were quick to point out that the single greatest variable for any cooling system is the temperature of the ambient air. Everything relates to the ambient air temperature. You should always record the air temperature at the track before you start jumping to conclusions about your coolant temperatures.
At the end of the day it seems that people worry entirely too much about coolant temperature. Running a racecar with a 160 degree coolant temperature probably won’t happen. Even if it happens it’s not a good idea. Cooler is not necessarily better. You need to be in the 210 degree range. Heat is a good thing. Especially when you’re dispersing all of that thermal energy back into the atmosphere. Remember your radiator has only one purpose – getting all of that thermal energy out of your car. You need to make sure all of the little components are operating at their optimum as well. Sometimes it’s not the radiators fault.
Stant Corporation
1620 Columbia Avenue
Connersville, IN 47331-1696
800.822.3121 ext. 58330
C and R Racing
301 Cayuga Drive, Unit A,
Mooresville, North Carolina 28117
704.799.0955
DeWitts
275 Grand Oaks Dr
Howell, MI 48843
517.548.0600
