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Street Race Truck More... The Toolbox

Differences Between Downflow and Crossflow Radiators

9/14/2016

Radiators are offered in a two basic configurations which differ to fit the space available, add mounting rigidity and offer varying inlet and outlet locations. The two commonly used radiator designs are downflow and crossflow. Each design offers its own advantages and disadvantages.

Downflow

Downflow radiators have the tanks located at the top and bottom of the core. The coolant enters through the top tank and flows down through the core with the help of gravity easing the work load of the water pump. This design fits early cars and trucks well which have a tall but narrow width grille and radiator support. The downflow radiator also has the advantage of inlet and outlet placement. The inlets and outlets can be positioned in the center, left, right or anywhere in between.

The disadvantage to a downflow radiator is the radiator cap placement. Since the radiator cap must be positioned on the top tank it is exposed to the high pressure side of the cooling system. This significantly increases the need for the cap to vent off excess pressure. When the cap vents off excess pressure in a downflow radiator it almost always allows some coolant to escape the system, which is due to the cap location and extreme agitation of the coolant at the inlet. In order to reduce the chances of venting off excessive amounts of coolant we suggest using a higher pressure radiator cap on a downflow radiator. 15 to 25 psi radiator caps are typical for downflow radiators. A radiator cap pressure rating of less than 15 psi typically does not work well on a downflow radiator, especially in hot temperatures like 90°F and up.

Crossflow

Crossflow radiators have the tanks located on the left and right sides of the radiator. Coolant enters the radiator at one side and the water pump forces coolant through the core to the opposite tank of the radiator. This design works well in later cars and trucks with a wide grille opening.

The crossflow design allows the radiator cap to be positioned on the low pressure (suction) side of the system, allowing for lower pressure radiator caps to be used such as 7 to 20 psi. Another advantage to the radiator cap location on crossflow radiators is that when venting excess pressure it is more likely to vent off air from the system instead of coolant. This is due to less coolant agitation within the low pressure tank.

Crossflow radiators are an excellent choice for racing applications and hard to cool vehicles such as big blocks or boosted engines in street cars and hot rods. For circle track racing applications with increased cooling system demand a high pressure radiator cap between 22 and 32 psi is suggested.

Double Pass Radiator

Crossflow radiators are also offered in double pass or even triple pass design. These different designs enhance the radiators ability to cool by increasing the number of times the coolant passes through the core of the radiator. To read more about double and triple pass radiators check out this article: Single Pass, Double Pass, Triple Pass radiators; what’s the difference?

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