So on my long list of tangents, one of the more random things I considered was an electric radiator fan. The advantage of an electric radiator fan isn't necessarily that it is more efficient by itself or that it cools better (in many cases it is actually less efficient or is less powerful for cooling), but that it can be controlled by a computer than can more restrictively select when it is needed.
Most TJs are equipped with a stock belt-driven clutch fan. The fan always spins at low (~20%) of the engine speed when disengaged. When the clutch senses a predetermined air temperature of radiator exhaust, the clutch engages, and the fan begins to spin closer to the speed of the water pump pulley (~80%). This system works well almost all the time; however there is only one input that affects the engagement of the fan, and that is the temperature of the air flowing out of the radiator.
An electric fan is typically controlled by the computer, meaning it can have a wide range of inputs and logic trees, ranging from coolant temperatures, A/C demands, air temperatures, road speeds, and numerous other values. With careful selection of the inputs and logic trees, modest improvements in fuel economy and range can be found. In addition, the fan can also be selectively engaged in scenarios where it may be desirable, such as during high A/C demands at low road speeds.
The 2.4L TJ was equipped with a 2-speed electric fan; the 4.0L got the stock mechanical fan. On the 4.0L Rubicon models, the relay slots otherwise used for the 2.4L electric fan were instead used to drive the locker pumps.
Electric fan conversions are not well-received on this forum for several good reasons.
Novak offers a shroud/fan kit (FX3300-T) that uses a SPAL fan. SPAL Automotive builds a lot of OEM fans, and sells to the aftermarket on the side. Their fans are known for being OEM-quality and actually produce their rated numbers. Most of their fans are rated not only in open air, but also have performance curves published that show how they perform at increasing pressure drop across the radiator. Most aftermarket fans are rated only in free air, and often have very poor performance given any restriction, hence one of the issues. The SPAL fans are also sealed like OEM, and tend to have fewer service issues.
Regarding reason #1, I'm pretty confident the reason we don't see performance or fuel economy from most electric fan kits is because they are controlled much like a clutch-driven fan, and have only one or two inputs. As such, they are generally set up to turn on very often to be more conservative and avoid risk of overheating. In addition, they cannot be instructed to turn on due to other inputs (e.g., A/C load), so they really don't see the advertised fuel economy and power benefits typically seen in OEM builds.
You could spend major $$$ building a control system for an electric fan that would take into account all of those factors. Ultimately, you may even spend more than the cost of the fuel saved. With enough temperature sensors, maybe an arduino, a PWM controller, and a few other items, you could build a near-flawless control system to maximize engine cooling and A/C performance while simultaneously maximizing fuel economy.
But what if that control system already existed?
Does it???
According to the FSM, all TJs have pinouts on the PCM for a low speed fan module and a high speed fan control.
But my PCM is for a 4.0! Surely it doesn't have any programming for an electric fan.
Let's just check the software on VCM Editor...
Wait a second...
It does exist!
So looking at the options, you can select between a one-speed, two-speed, and three-speed relay fan, a two-speed PWM fan, a PWM for BLDC motor fans, and a continuously variable PWM fan. And of course you can turn it on and off.
However, changing the fan types does not change the control options in front of us. So we are stuck with the above control logic. But there is quite a lot we can play with here!
1st, we can select up to three independent fan speeds. However, given that we only know two of the pinouts for the relay controlled fan logic, I'm not sure it's going to be feasible to find that 3rd speed.
2nd, we can control when the fan enters those three speeds (plus turning off) based on:
My best guess on how to make this work would be to add two pin receivers to the OEM PCM wiring harness (the slots for the 4.0 are empty, but the pins are there on the PCM). The high speed wire (Pin 6) goes to a large relay that turns the fan on, and the low speed wire (Pin 4) goes to a large relay with some sort of speed reducer, maybe a large resistor. Perhaps one of the unlabeled pins is for the 3rd fan speed.
So has anyone ever tried something like this? Thoughts?
Most TJs are equipped with a stock belt-driven clutch fan. The fan always spins at low (~20%) of the engine speed when disengaged. When the clutch senses a predetermined air temperature of radiator exhaust, the clutch engages, and the fan begins to spin closer to the speed of the water pump pulley (~80%). This system works well almost all the time; however there is only one input that affects the engagement of the fan, and that is the temperature of the air flowing out of the radiator.
An electric fan is typically controlled by the computer, meaning it can have a wide range of inputs and logic trees, ranging from coolant temperatures, A/C demands, air temperatures, road speeds, and numerous other values. With careful selection of the inputs and logic trees, modest improvements in fuel economy and range can be found. In addition, the fan can also be selectively engaged in scenarios where it may be desirable, such as during high A/C demands at low road speeds.
The 2.4L TJ was equipped with a 2-speed electric fan; the 4.0L got the stock mechanical fan. On the 4.0L Rubicon models, the relay slots otherwise used for the 2.4L electric fan were instead used to drive the locker pumps.
Electric fan conversions are not well-received on this forum for several good reasons.
- The kits don't really provide any significant benefit in power, cooling, or fuel economy. Since they are controlled by a single (sometimes two) inputs, they don't have much better control systems than a mechanical clutch fan.
- The most commonly used aftermarket kits use cheap parts that don't provide the rated figures, and often don't last very long.
Novak offers a shroud/fan kit (FX3300-T) that uses a SPAL fan. SPAL Automotive builds a lot of OEM fans, and sells to the aftermarket on the side. Their fans are known for being OEM-quality and actually produce their rated numbers. Most of their fans are rated not only in open air, but also have performance curves published that show how they perform at increasing pressure drop across the radiator. Most aftermarket fans are rated only in free air, and often have very poor performance given any restriction, hence one of the issues. The SPAL fans are also sealed like OEM, and tend to have fewer service issues.
Regarding reason #1, I'm pretty confident the reason we don't see performance or fuel economy from most electric fan kits is because they are controlled much like a clutch-driven fan, and have only one or two inputs. As such, they are generally set up to turn on very often to be more conservative and avoid risk of overheating. In addition, they cannot be instructed to turn on due to other inputs (e.g., A/C load), so they really don't see the advertised fuel economy and power benefits typically seen in OEM builds.
You could spend major $$$ building a control system for an electric fan that would take into account all of those factors. Ultimately, you may even spend more than the cost of the fuel saved. With enough temperature sensors, maybe an arduino, a PWM controller, and a few other items, you could build a near-flawless control system to maximize engine cooling and A/C performance while simultaneously maximizing fuel economy.
But what if that control system already existed?
Does it???
According to the FSM, all TJs have pinouts on the PCM for a low speed fan module and a high speed fan control.
But my PCM is for a 4.0! Surely it doesn't have any programming for an electric fan.
Let's just check the software on VCM Editor...
Wait a second...
It does exist!
So looking at the options, you can select between a one-speed, two-speed, and three-speed relay fan, a two-speed PWM fan, a PWM for BLDC motor fans, and a continuously variable PWM fan. And of course you can turn it on and off.
However, changing the fan types does not change the control options in front of us. So we are stuck with the above control logic. But there is quite a lot we can play with here!
1st, we can select up to three independent fan speeds. However, given that we only know two of the pinouts for the relay controlled fan logic, I'm not sure it's going to be feasible to find that 3rd speed.
2nd, we can control when the fan enters those three speeds (plus turning off) based on:
- Coolant temperature
- Road speed
- A/C system pressure
- Transmission temperature
My best guess on how to make this work would be to add two pin receivers to the OEM PCM wiring harness (the slots for the 4.0 are empty, but the pins are there on the PCM). The high speed wire (Pin 6) goes to a large relay that turns the fan on, and the low speed wire (Pin 4) goes to a large relay with some sort of speed reducer, maybe a large resistor. Perhaps one of the unlabeled pins is for the 3rd fan speed.
So has anyone ever tried something like this? Thoughts?
