What You Need To Know About Air Flow
Many a debate has been held relating to air flow in an engine’s cooling system and what is an adequate volume of air and what is not. One fact is, we have never had any calls on any level complaining of too much air coming through a radiator core! The purpose of a radiator is to assist with the transfer of heat from the core to the air via the coolant flow to and from the engine. For this reason, one of the most crucial factors in a cooling system is ensuring there is adequate and efficient air flow; lack of air flow can affect the effectiveness and efficiency of a radiator and indeed the longevity of an engine. Maintaining adequate air flow at various speeds is essential and can be complex. A radiator needs to have a solid and consistent stream of air passing through it on most occasions while the engine is in operation. The front opening, air intake is one key aspect to its performance. Ideally, the radiator needs to be squared up to the air. Scoops, lips, deflectors and recessed panels can be used to improve air flow when the frontal area of a vehicle is less than ideal.
The next issue relating to air flow that requires serious attention is the fan. Engine-driven fans MUST have a circular shroud to be fully effective. The blades should have no more than 1” clearance to the shroud. Some OEM mechanical engine-driven fans can reach a blade stall at high RPM, causing a ‘wall’ that prevents air from passing through it. Hence the installation of a temperature-controlled, radiator mounted electric fan, in the majority of cases, as a replacement, is far more efficient. To function efficiently the air stream on the front side of the radiator/needs to be higher than the air stream behind it. The higher pressure is used to drive the air through the radiator core. If there’s a buildup of air pressure in the fan cowling or engine compartment, air flow across the radiator can stall, causing higher engine temperatures. For this reason, thoughtful consideration should be given to vehicle’s use for both low speed cruising and higher speed operation to ensure the effective channeling of air to the radiator while operating in both circumstances.
Nearly all modern-day vehicles have an electric, temperature-controlled fan installed as standard equipment at the rear of the radiator. All modern electric fans are supplied with a standard circular shroud to maximise efficiency. Attention should be given to the power (watts) of the fan motor and the published (CFM, Cubic ft3/min), wind force the specific fan produces, usually the larger the electric fan the higher the CFM. Australian manufacturer, Davies Craig publishs all the specifications and dimensions of the entire range of 12v & 24v Thermatic Fans and Thermatic Switches on their website, www.daviescraig.com.au
Some electric fan models may be enclosed in a metal or nylon cowling (sometimes referred to in some circles as a shroud) which is purposefully designed to be mounted on the rear of the radiator, only. While driving at speeds of 60kmh or under, electric fans are most effective due to their total operating independence from engine revs. With a clear air intake in front of the radiator driving above 60kmh a fan is not as necessary. The use of a cowling can be problematic as encompassing the entire rear radiator core can inhibit air flow at speed. If there is a build-up of air pressure in the fan cowling or engine compartment, air flow across the radiator can stall, causing higher engine temperatures.
For example, an electric fan and cowling that covers the entire core should have "trap
doors", usually made of silicone, rubber or nylon, installed to assist with cooling efficiency. When cruising at low speed these trap doors will stay closed to prevent bypass. While at speed, the doors will open to allow more air flow and prevent the cowling from damming the air. Since the engine compartment must be able to maintain pressure differential as a vehicle’s speed increases, many original equipment manufacturers install air dams or other wind deflector devices to increase the pressure at the face of the radiator and block the air from passing under the car.
In conclusion, an electric fan’s operation is NOT ‘complete’ without an appropriate Digital Thermatic Switch. It is vital the electric fan is automatically activated when the engine temperature reaches the manufacturer’s thermostat temperature and the heat transfer of coolant leaves the engine to the radiator or in case one is using a Davies Craig LCD EWP/Fan Controller, the electric fan/s will activate at +3c above your set/targeted temperature which again, should be set at the OEM’s thermostat temperature. There are too many stories of ‘cooked’ engines when the vehicle owner forgot to activate the manual override switch. Remember the temperature gauge in the vehicle is a ‘guide only’ and by the time this information has made it to the gauge the engine temperature may have risen to a critical level.