In a single-pass radiator the fluid flows through the radiator a single time. A double-pass radiator has two separate sets of tubes, sometimes seperated by a baffle, other times with one set stacked behind another set. Radiators with that second setup are known as a two-core setup. In either case, the fluid flows through one set of tubes and then comes back across the other set, essentially flowing through the radiator twice, hence double-pass. Obviously, in a three-pass there are three separate sets (or cores) of tubes sandwiched together while the four has . . . you guessed it, four cores.

The downside to multi-stack radiators is when you stack cores one behind the other you make it harder and harder for air to flow through the radiator. For bigger tracks and higher speeds, three- and four-pass systems are fine, but they just won't flow enough air to cool your engine efficiently in a 20-lap feature on a flat 1/3-mile track.

Fins - How tightly packed the fins are in your radiator is known as fin count and is measured in fins per inch. A higher fin count means there is more surface area for the aluminum to radiate the heat it absorbs from the water/fluid into the air. However, if the fin count is too high for your application it can actually form a barrier to the air trying to pass through the radiator. When this happens the air stacks up in front of the radiator or moves around it and doesn't reach the cooling tubes in the second row.

As a general rule, a fast race car can use a higher fin count while slower cars should use a lower fin count. If you're racing on tracks between 3/10- to 1/2-mile in length you should look for 14-18 fins per inch.

Shrouds - Regardless of the type of car you race you should have some type of shroud on the radiator. They are easy to fabricate and will maximize your airflow. Shrouds in front of the radiator direct the high pressure incoming air directly to the fins/core. Shrouds between the radiator and mechanical fans help to increase the airflow through the radiator. Sealing the shroud with duct tape is important to prevent any of the air from escaping.

Air Temp Influences - It's not unheard of, and actually probably more common than any of us realize, for the cooling system that worked like a champ in early spring to give up the ghost come mid-July. Here's why: The radiator works the same regardless of the ambient temperature.

"A good rule of thumb is for every 10 degrees increase in the outdoor temperature, the fluid will be 10 degrees warmer in the motor," says Richard Bailey owner of Innovative Cooling Equipment (ICE) of Concord, N.C.

Based on an outside temperature increase from 80 degrees to 105, you will experience a 25-degree increase in fluid temperature in the motor. Take it a step further, let's say your motor typically runs at 220 degrees. Add 25 degrees to that and you're at 245 and in danger of overheating.

That brings us to radiator selection. Your pick of a radiator should be based on the highest temps you'll see during the racing season. However, you must remember that the radiator is just one part of your overall cooling system. That system should be designed and installed not only based on those high outside temps but also on the number of laps you race, the size of your track, and the horsepower of your motor.

When looking for a new radiator, choosing the right number of passes is crucial. Many racers attribute overheating or running hot problems during the summer months to the increased ambient temperatures in June, July, and August. Often the problem rests within a poorly maintained cooling system, a mismatched radiator for your application, or a system that flows the fluid either too quickly or too slowly through the radiator.

So what exactly determines the proper number of passes? What and where you race is probably the biggest factor.