Practical Automotive Maintenance: Fans

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Fans

08.32

00:00	Radiator fans are a key part of the cooling system, helping us keep the engine at the right temperature, especially at low speeds.
00:07	They're typically mounted behind the radiator or any other heat exchanger on the car and strategically positioned to pull air through the fins, cooling them down and increasing our radiator's ability to efficiently dissipate heat and keep our engine from overheating.
00:23	The ability of a fan to move air is measured in CFM, which stands for cubic feet per minute, and it's a volumetric measurement that quantifies the amount of air moved through a given space in one minute.
00:36	In the context of automotive cooling fans, CSM represents the fan's capacity to push or pull air through a vehicle's heat exchanger, directly affecting the cooling system's efficiency and the engine's temperature regulation.
00:50	This measurement serves as a critical specification when selecting appropriate cooling solutions.
00:55	A higher CFM means more air is moved by the fan and this increases the likelihood of efficient cooling.
01:03	Conversely, the lower the CFM, the less air is moved by the fan, reducing the likelihood of efficient cooling.
01:09	This is only one of the many factors that make up an efficient system, and we'll cover the rest as we go through this module.
01:16	Generally, fans have a shroud either surrounding them or incorporated into the design, making them a single unit.
01:22	The shroud plays a critical role in directing airflow.
01:25	Ensuring that air is pulled evenly across the surface of the radiator or heat exchanger, rather than just through the area immediately in front of the fan blades.
01:34	Without a shroud, airflow becomes turbulent and inconsistent, leaving dead zones where little to no, cooling takes place.
01:42	By creating a seal and guiding the air, a well -designed shroud maximizes cooling efficiency.
01:48	In many applications, the design of the shroud is just as important as the fan itself, as poor shroud design can undermine the performance of even the most powerful fan.
01:57	Let's now discuss the two main types of fans used in our cooling systems, known as viscous and electric.
02:03	We'll start with viscous fans, which connect directly to the engine through a fluid coupling that increases engagement as the engine temperature rises.
02:12	In simple terms, when cold, the viscous hub allows slip, so that the fan spins slower, reducing mechanical load on the engine as airflow isn't needed when the engine is cold.
02:21	As the engine warms up to operating temperature, the viscous coupler locks up, and this increases the fan speed, and as a result, a larger volume of air is pulled through the radiator.
02:32	Viscous fans offer significant advantages through their mechanical simplicity, consisting only of a fan blade bolted to a hub that's then bolted to the engine.
02:41	This requires no additional electrical components, is easy to install, and generally provides reliable operation in all conditions, with no servicing required.
02:50	However, the mechanical connection does have some minor drawbacks.
02:55	Because the fan is driven by the engine, this causes something called parasitic loss, which is mechanical drag or resistance, resulting in a small power loss.
03:04	Cooling capacity also only varies with the engine speed, rather than the actual temperature of the system.
03:11	During slow speed operation in hot conditions, viscous fans can place disproportionate loads on the engine, potentially providing a less than optimal amount of airflow.
03:21	It's worth mentioning that some much older vehicles lack viscous hubs, and the fans are directly bolted to the water pump or the fan pulley driven by the engine, meaning that the fan speed is locked to the rpm of the pulley it's attached to.
03:34	However, this is likely irrelevant for 99% of the vehicles we'll come across today.
03:40	Viscous or solid style fan blades were originally made from steel, however, modern vehicles now use plastic blades to help save weight, reduce cost, and reduce mechanical load on the engine.
03:50	With a couple of exceptions, transverse engines, also known as east-west engines, where the front pulley section faces the side of the chassis, are generally unable to use mechanical fans.
04:02	As not only is there usually no room, but this would mean that the fan is nowhere near the radiator, which is typically right in the front, rendering its operation useless.
04:10	The majority of today's vehicles will have an electric fan or fans.
04:15	As the name suggests, these fans are driven by an electric motor instead of mechanically driven by the engine.
04:21	These are typically relay operated and switched by the engine control module, with the ability to be used at variable speeds based on the coolant temperature.
04:30	Electric fans are typically bolted straight to the back of the radiator via a fan shroud.
04:35	These are independent of the mechanical pulleys, allowing for much less parasitic loss, providing precision control regardless of the engine speed, and can continue functioning after engine shutdown to prevent heat soak in radiator cores.
04:48	These fans are non-operational on cold start, only kicking in once the thermostat has opened and the engine is up to operating temperature.
04:56	At this point a low speed fan will kick on and then turn off anytime our temperature drops below a threshold determined by the manufacturer.
05:04	It's worth noting that while this is the norm now, older style electric fans don't vary speeds, they simply switch on or off as necessary.
05:12	These on and off points are actually different by around two degrees, which prevents the fan from rapidly cycling on and off if the temperature is sitting at the switching point.
05:21	For example, the fan may switch on at 94 degrees and not switch off until 92 degrees.
05:28	This is known as hysteresis.
05:30	Fan layouts also vary.
05:31	It's common to see one large fan or alternatively a pair of smaller fans.
05:35	Large singular fans are sometimes variable speed and controlled with pulse width modulation.
05:41	This is a method of controlling power delivery to an electrical device by varying the duty cycle of an electrical signal.
05:49	Think of this as a dimmer switch for your lights.
05:51	Electric fans found in pairs usually have singular and independent speeds.
05:56	With one being a low speed fan activated at operating temperature and the other being a high speed fan set to come on once a higher temperature threshold has been reached.
06:05	We'll also see further distinction between electric fans with the option for what's called brushed and brushless motor technologies.
06:12	Both have their pros and cons.
06:14	So, we'll go through that now.
06:16	Brushed motors use carbon brushes and a commutator to transfer current to the rotor.
06:21	The brushes physically contact a part known as a commutator, creating friction and wear over time.
06:26	This physical contact and wear created a limited service life of approximately 8, 500 hours.
06:34	Additionally, these carbon brushes can generate sparks during high speed operation which are capable of creating electronic interference.
06:42	Brushless DC motors are an improvement on this technology with a different design.
06:47	As the name suggests, the use of the brushes that physically contact other components are removed.
06:52	Instead, using windings as the stator while permanent magnets function as the rotor.
06:57	Brushless fans last up to five times longer than brushed ones and provide steadier, quieter performance with high airflow across all pressure ranges.
07:07	Generally, an OEM fan does a great job of moving enough air when the vehicle is stationary or traveling at low speeds.
07:14	So, situations where we may want to consider upgrading systems are if we're fitting a new radiator that's not compatible with the stock fan, we're replacing a viscous with an electric fan, or we need to make room for something like an aftermarket turbocharger kit.
07:29	A significant size increase in radiator cores or stacking of multiple coolers in front of one another can also affect the fan's efficiency due to the increased surface area it now has to service.
07:40	We covered a lot in this module.
07:42	So, let's go over the key points before moving on.
07:45	Fans are essential for maintaining engine temperature, especially at low speeds.
07:49	Most are mounted behind the radiator to pull air through the core, with efficiency measured in CFM or cubic feet per minute.
07:58	The two main types are viscous and electric.
08:00	Viscous fans use a fluid coupling to adjust engagement based on temperature.
08:05	They're mechanically simple, but create parasitic engine drag.
08:09	Electric fans operate independently of engine speed.
08:12	Electric fans are available in brushed and brushless form.
08:15	Brushless fans offer longer life, better efficiency and quieter operation.
08:19	Fan shrouds are also crucial in directing airflow evenly across the radiator.
08:24	Both fan selection and shroud design play a key role in effective engine cooling.