Keeping Cool

Radiators

The radiator is really the core of the cooling system, as this is where the heat generated by the engine is removed from the system. There are two main styles of radiators used in conventional passenger cars: cross-flow and down-flow. The terms refer to the direction of coolant flow through the radiator. Radiators are generally rated in terms of core dimension and the number of rows of tubes used--larger cores and more tubes obviously mean increased capacity. The most common materials for radiators traditionally have been a combination of brass and copper, but modern units are often aluminum.

Down-flow radiators have tanks above and below the core with coolant tubes running vertically between the two. Coolant enters the top tank and flows downward to the bottom before re-entering the engine. This arrangement worked acceptably in older cars that were tall and narrow, but as hood lines dropped, radiator profiles had to be reduced. Generally, there does not seem to be a major difference in thermal performance between cross-flow and down-flow radiators.

Cross-flow radiators have tanks on either side of a core of horizontally stacked tubes, which allows the tubes to be longer, giving the coolant more time to exchange heat on each pass through the radiator. An added benefit is that the radiator cap can be positioned on the "suction" or "low-pressure" side of the radiator--the tank that receives coolant after it has passed through the core. The low-pressure/low-velocity environment in this tank allows the air to separate from the coolant and bleed off first when the cap's blow-off valve is activated by excessive pressure in the system.

Regardless of the configuration of the radiator, the number of rows of tubes is usually a variable. Generally, the more tubes the better, as they increase cooling capacity. To determine how many rows your radiator has, it may be necessary to look inside the filler neck, as many OE radiators use the same tanks and framing with all tube variations. This can make a single-row radiator appear like a heavy-duty unit. The radiator shown is a two-row design.

Traditionally, radiators have been made from brass and copper, but many modern radiators are now made with aluminum. The auto manufacturers use aluminum primarily because it's lighter and cheaper than brass/copper, though the aftermarket touts aluminum as a cooling benefit. This has raised controversy since copper and brass are both better conductors than aluminum, which should allow them to transfer heat more efficiently. However, the increased strength of the aluminum allows manufacturers to make wider tubes, increasing the primary cooling surface and raising cooling capacity of radiators of this type.