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Street Race Truck More... The Toolbox

Fan Shrouds - A Critical Cooling System Component

9/14/2016

You may think some of the things in your engine bay are pointless, like that fan shroud on the back of your radiator. We are here to tell you: LEAVE it there!

You may think that a shroud is a useless piece of plastic or metal, but they really do serve a purpose. They focus airflow through the entire radiator as compared to just the area that is covered by the traditional fan, creating a vacuum that pulls air across the entire surface area of the radiator, thus increasing cooling.

An un-shrouded fan is moving air through only the portion of the radiator equal to the surface area of the fan. See where we are going with this? If you spent the last week rebuilding your classic’s engine, would you really want to fry it because you didn’t think that shroud was needed? We thought not.

Let’s do a little math, shall we? (Don't worry, we did it for you!)

To calculate the area that is covered by your fan, use the formula below. As an example, we'll use a 17" diameter fan.

Area = (Pi) x (r2)

  • Area = (3.14) x (8.52)
  • Area = (3.14) x (72.25)
  • Area = 226.85”2

Now, for comparison, use the formula below to calculate the surface area of your radiator. We'll use a 27” tall universal radiator with a core height 22.25” and a core width 18.25” for this example.

  • Area = (Height) x (Width)
  • Area = (22.25) x (18.25)
  • Area = 406”2

Judging from the calculations above, you can see that without a shroud directing the airflow across the entire radiator, you are effectively not using 44% of your radiator. By simply adding the proper size shroud behind your radiator, you'll ensure that 100% of the radiator's surface area is used to cool your engine.

And here are a few more tips related to radiators and shrouds:
  • All shrouded fans should be on the engine side, no exceptions.
  • Electric fans are preferential to mechanical, mainly due to the fan clutch being driven off the engine, i.e., no mechanical power draw when the fan kicks on.
  • NEVER use the radiator as a ground. Electrolysis can result and it can destroy your radiator.
  • A commonly held thought is that fan blades should recess 50% into the shroud for optimum cooling. To get your fan in the correct position, use fan spacers or shims.

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