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Down flow versus cross flow radiator

Advantages and disadvantages of down flow versus cross flow radiator

Two types of car radiators

Car radiators are available in two types; down flow versus cross flow radiator. The names refer to how the coolant travels through the radiator core tubes. Down flow radiators rely on gravity to move the coolant from the top tank to the bottom tanks, while cross flow radiators rely on the characteristic of fluid to seek it’s own level.

cross flow radiator

Typical cross flow radiator

down flow radiator

Typical down flow or vertical flow radiator

Radiator construction

Older radiators were built with a copper inlet and outlet tank and either a copper or aluminum core. However, most modern radiators are built with plastic tanks and an aluminum core. Thin tubes transport the coolant from one tank to the opposite tank. Folded fins fill the space between the tubes and help transfer coolant heat from the tubes to the air passing through the radiator core.

Radiator cap placement

In designs where the pressure cap is located on the radiator

coolant flow through a cross flow radiator

Hot high pressure coolant enters the inlet tank and flows across the tubes to the outlet tank. Airflow across the tubes cools the coolant and lowers both the temperature and pressure. Since the radiator cap is on the outlet tank, high RPMs won’t cause a pressure release

itself, the cap must always be on the top tank (high pressure) in a down flow radiator. However, the cap on cross flow radiator can be located on the suction or low pressure side of the radiator, opposite the upper radiator hose.

Advantages of Cross Flow Radiator

In modern vehicles with an aerodynamically shaped hood, there simply isn’t enough room to accommodate a tall down-flow radiator. So cross flow radiators are used to accommodate body design. They’re shorter but wider than a comparably sized down flow radiator.

Because the pressure cap can be located on the low pressure tank, the design prevents premature pressure cap opening caused when a high flow water pump runs at high engine RPMS.

Because cross flow radiators are wider, they are often cheaper to build, owing to the fact that this design requires fewer tubes and thus fewer weld/solder joints.

If the cross flow radiator can be mounted so the pressure cap is higher than the engine, the radiator is self bleeding. However, if the radiator is placed lower than the engine, a surge tank or bleed line is required.

Disadvantages of Cross Flow Radiator

The biggest disadvantage of a cross flow radiator is its width, making it a bit more difficult to fit in an engine compartment. Designers must ensure that enough outside air enters the grille area and distributes to the extreme ends of the cross flow radiator. In addition to the space limitation, cross flow radiators often have less coolant capacity than a down flow radiator.

dorn flow versus cross flow

A cross flow radiator takes up more side to side space, while a vertical flow radiator requires more height

Because cross flow radiator rely on a fluid’s ability to seek its own level, cross flow radiators often have a higher temperature differential between the inlet and outlet sides. That higher temperature differential can cause joints on the radiator to break and leak or allow air into the system.

Advantages of a down flow radiator

They’re narrower than a comparably sized cross flow radiator. If width is an issue and you have the height, a down flow radiator may be your best option.

Disadvantages of a down flow radiator

Aside from its taller height, the single biggest disadvantage of a down flow radiator is the fact that the pressure cap is always located on the top tank. This is the hottest part of the radiator with the highest internal pressure. At high engine RPMS, the combination of high heat and high pressure can force the pressure cap to open and bleed pressure and coolant into the recovery tank.

©, 2017 Rick Muscoplat

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Posted on by Rick Muscoplat


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