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7 data points you'll need to select the right engine cooling fan

October 21, 2020

From engine envelope size to required airflow, there are a bevy of inputs necessary to find the right cooling fan for a truck, tractor, excavator or other heavy-duty application.

Here's a quick checklist design engineers can use to get started.

1. Airflow criteria

This is the most natural place to start. What are your airflow requirements, both in terms of volume and pressure?

2. Diameter

Based on fan shroud size and the positioning of other vital components, fan size differs from engine to engine. How much space do you have to work with?

3. Desired fan speed

How fast do you want the fan to spin, based on airflow requirements and operating conditions? Your fan supplier should be able to help you with this determination.

4. Rotation and direction

Fans can turn either clockwise or counterclockwise, and "suck" air toward the engine or "blow" air away from it. That makes for four different rotation-direction options: clockwise blower, counterclockwise blower, clockwise sucker and counterclockwise sucker.

5. Fan configuration

What kind of shroud are you thinking about using? Standard options include a Venturi shroud or a flat orifice plate. You'll also want to pick a desired blade count, fan immersion, and tip clearance, which is calculated as a percentage of the overall fan diameter. For example, a 10-inch fan with a 1.5-percent tip clearance would be 0.15 inches away from the shroud.

Best practice for immersion is 1/3 of the fan outside the shroud for sucker fans, and 2/3 out for blower fans. Tip clearance should usually be about 1.13-1.5 percent of the fan diameter.

One other important thing to note: If the engine or another obstruction is located immediately downstream from the fan, this will determine which fan configuration is best. 

6. Air conditions

These will vary by application type. Obviously, a long-haul truck based in California faces a lot different air conditions than a wheel loader operating year-round in Canada. Consider factors that affect air density like operating temperature, altitude, and relative humidity.

7. Fan drive type

Fans perform best when paired with the proper on/off, two-speed or variable-speed fan drive. You can learn more about the different types here.