The Purpose of Automotive Cooling Fans: Choosing the Right Fan

If you’ve ever noticed how quickly the temperature gauge in your car or truck rises in the summer, then you understand just how important it is to keep your engine temperatures under control.

Normally aspirated engine temperatures can approach 120°C on a hot day, while turbocharged engine temperatures may reach as high as 150°C. And make no mistake: these are temperature ranges where poor heat transfer will start to rob your engine of performance while also increasing the risk of parts failure.

Your vehicle’s radiator and water pump are responsible for keeping your engine adequately supplied with coolant at all times, but they can’t handle the job of cooling alone. Cooling fans are responsible for moving large quantities of cool, low-pressure air through the radiator, and there’s nothing coincidental about their design, selection, or placement. They’re a lot more purposeful than they appear, so let’s take a look at just how much of an impact they have on engine cooling.

car cooling fan
source: cashcarsbuyer.com

Choosing the Right Fan to Keep Your Car’s Engine Cool

From simple water pump-mounted flex fans to fully shrouded dual- and triple-fan assemblies, there are high-volume automotive cooling fans available for every type of engine, environment, and application imaginable. And the fact that there are so many different types of fans on the market speaks volumes for how important they are, and the kinds of questions that you need to ask yourself before buying one, including:

·   Do you prefer to mount a fan behind or ahead of the radiator?

·   How much space do you have available?

·   How much airflow does your actually engine need?

·   Do you intend to use it as a primary or auxiliary?

·   How do you want to control it?

These questions don’t always have simple answers, but being able to distinguish between the different types of cooling fans can answer most of them. That starts with deciding whether you prefer having your car cooling system fan powered by your engine or your battery.

Getting Familiar With Cooling Fan Drive Types

There are 2 types of fan drives: mechanical and electric. Both can have either straight or S-shaped blades, or be made from steel or plastic, but the real difference between them comes from how much power they draw, and where they draw it from.

car cooling fans
source: vintage-mustang.com

Direct Drive Mechanical Fans

 Mechanical fans are driven directly by the engine’s rotation and are mounted behind the radiator. Flex-type mechanical fans rotate at exactly the same speed that the engine turns, while clutch-type mechanicals are mounted on a thermostatically-controlled hub that allows the fan to rotate according to the engine’s temperatures.

Mechanical car cooling fans have been used for decades on V- and inline-type engines, can easily reach up to 19” in diameter, and are virtually unbreakable. They can take up significant space under the bonnet though, and can also be a drag on horsepower at high RPMs. The tradeoff, however, is that in ultra high-performance applications, flex-type mechanicals will continue to draw cooling air at any speed the engine is capable of turning.

Externally Powered Electric Fans

 12V or 24V electric fans can be mounted either behind or ahead of the radiator, and are driven by their own DC motors. And because they’re not powered directly by the engine, they can be set up in single, double, or even triple fan configurations that are independently controllable via relays or temperature sensors. An electric fan setup will let you freely take your dual fan 4WD off-road, turn the fans off temporarily, and not worry about them drawing in nothing but dust and mud.

Depending on the configuration, the fans in electric car cool systems can be just as large as their mechanical counterparts, while still leaving extra space for aftermarket turbos, air filters, and other accessories. Their lack of reliance on engine speed makes them ideal for maximum cooling at low and mid-range RPM, but they can be a load on weak charging systems, and shouldn’t be relied on as primary fans on thicker, 4-tube radiators.

Recognizing Whether a Cooling Fan is Pushing or Pulling

Cooling fans are designed to either push or pull air through a radiator. Some electric fans are reversible, and are capable of either pushing or pulling air. An optimized fan cooling system would ideally consist of a primary puller aided by an auxiliary pusher.

car radiators
source: cashcarsbuyer.com

Upstream Pusher Fans

Pusher fans are mounted ahead of the radiator and push air through it. They’re usually the preference for modified vehicles because of the space they’re able to free up immediately ahead of the engine, and by the nature of their location are always electric driven.

With their largely unimpeded airflow, pusher fans normally provide better cooling for cars at low speeds. Their forward positioning, however, can also restrict valuable airflow when moving at high speeds.

Downstream Puller Fans

Puller fans pull air through the radiator from behind, and can be either mechanical or electric driven. These fans have no impact on the radiator’s airflow; and with the ability to use them with shrouds, are considered to have greater cooling capacity.

Puller fans typically take up the most space under the bonnet though, and can make the installation of larger aftermarket accessories like breather boxes and intercoolers more of a challenge. When space is not an issue though, puller fans provide the all-around auto cooling advantage.

Airflow is The Key to Keeping Cars Cool   

The most important aspect of cooling fan selection is the airflow rate. Fans are rated by the maximum CFM (cubic feet per minute) of air they can push or pull, and most manufacturer-rated guidelines suggest the following minimums for stock, unmodified vehicles:

·   1,250 CFM for 4-cylinder engines;

·   2,000 CFM for 6-cylinder engines; and,

·   2,500 CFM for 8-cylinder engines.

automotive cooling system
source: keithcoxautobahn.com

A tightly wound, 400HP twin-turbo 4-cylinder, however, will inherently need more cooling than most 6-cylinder utes, so having an idea of how much horsepower your engine is producing can help you calculate the CFM for your car’s cooling system more accurately. A fan that can’t provide sufficient airflow for your engine’s cooling requirements or operating environment is ineffective, which is why you always want to use the largest CFM fan that’ll fit.

Basic Cooling Fan Installation Points

Once you’ve considered the drive type, upstream or downstream attributes, and the required CFM, measuring and carefully assessing the area where you decide to mount the fan is the last requirement. A few final points that you’ll want to keep in mind, especially if you spend a lot of time off-road where things are prone to excessive movement, would include:

·   Ensuring that there’s adequate clearance between the cooling fan and the radiator;

·   Ensuring that the forward-facing cooling area is as free from obstruction as possible; and,

·   Utilizing a radiator fan shroud whenever possible.

Bear in mind too that regardless of the type or CFM of the cooling fan, a correctly sized radiator is still the most important component of the entire cooling system. With the right radiator, selecting the right cooling fan is going to be a lot less complicated.   

The Final Word

At the end of the day, selecting a good aftermarket cooling fan isn’t difficult, but it takes looking at all the possibilities to make the best choice. A fully shrouded, dual pulling fan setup is going to look good and draw in tons of fresh air, but it might not give you the added space you need for other accessories that a new pusher setup would. 

No matter what your preference is, you can be confident that there’s a high volume automotive cooling fan available that’s going to fit your requirements perfectly; and choosing the right one can turn out to be one of the best decisions you’ve ever made for protecting your engine.