As promised I decided to post an objective view or actually a balanced view on running an \'Electric Fan as a modification\'......
It\'s gonna make some reading, but please have a read as hopefully it makes sense and you will understand and like me learn something.....
The cooling system consists of 5 basic parts: the engine, the water pump, the radiator, fan and the thermostat. Water passages inside the engine are filled with a coolant/water mixture (commonly just called "coolant"). These passages allow the heat that is generated within the engine to transfer into the coolant. Coolant is circulated through the engine via a water pump, which is driven from a belt off of the main eccentric shaft pulley. The stock fan and fan clutch assembly also mounts of the shaft of the water pump, and is therefore driven by the engine as well. The pump\'s job is to circulate water though the engine and the radiator. Air flowing over the radiator cools the coolant, and thus the engine. A thermostat is used to open or close flow of coolant through the rad to maintain the engine temperature at a constant (90 C).
The stock clutch fan is attached to the water pump shaft. This shaft receives it\'s rotation from the engine itself. The fan is not directly attached to the shaft, it is actually bolted to a viscous clutch. The clutch then sits between the fan and the shaft. The purpose of the clutch is to keep the fan at a (fairly) constant speed, and to only engage the fan when it is needed.
"Think of the clutch as a very simple mini torque converter." Inside is a fluid. When this fluid is cool, the clutch is freewheeling, and thus the fan turns relatively slowly as the clutch slips. As the engine heats up, so does the clutch as hot air from the rad flows over it. The fluid thickens up, engaging the clutch and turning the fan at engine speed up to about 2000 RPM. At this point, it begins to slip again to keep the fan at the most efficient speed.
In which, more air flows through the rad, cooling the engine. The clutch cools down as the engine does, and then disengages. Thus, the cycle repeats
What\'s important to note is that the fan is only used when the engine is idling, or the car is creeping along at low speed (less then 20 MPH). If the car is stationary or creeping, there is not enough natural airflow through the rad to provide adequate cooling. Thus, the necessity of a fan.
Thats the basic operation of the Stock Fan......... Now the Electric fan.
The most common misconception is that the electric fan cools better then the stock. People see the high CFM numbers in the catalogues (for example, the Black Magic is advertised as pulling 2,800 CFM, and the Perma Cool "finger chopper" is advertised at 2,950 CFM) and are impressed. The truth is that no one actually knows the CFM rating of the stock fan.
It has simply never been measured by anyone but Mazda/or specific car type manufacture. All we do know is that it is rated at "a lot". And to be honest, who cares how much air the stock fan moves? It is more then adaquate as long as it\'s clutch and the rest of the cooling system is in good shape. The steeply raked blades of the stock fan move quite a lot of air, even if it turns slower then an aftermarket electric unit.
Experience has shown that when in good shape, the stock fan is even easily capable of handling a 400HP engine (aftermarket rad installed).
Many people also seem to believe that an electric fan will cure their "at speed" overheating problems. "Recall that the fan is not even used when at speed," as the natural flow of the of air through the radiator is more then enough (much more then a fan, in fact) to keep the car cool.
But naturally we are not necessarily after better cooling. We want POWER big BHP\'s, and we see Electric Fans selling and saying/claiming "10-20 free BHP!" by converting to an electric fan. Well, that\'s simply not true. There will be a horsepower gain for sure, on the order of 0.5 - 2 BHP(max) .
Remember that the electric power to run the fan must come from somewhere, and that somewhere is the alternator. Electric fans draw quite a lot of current. Most pull surges of 35A or more to start up, then run at 8A-10A. This puts extra load on the alternator.
Ever pedaled a bicycle with a generator powered light? If so, then you will know that as the electrical load on a generator/alternator increases, the generator/alternator becomes harder to turn.
Now suddenly, all that "free" HP you just freed up is once again being used. This time, though, it is being used to turn the alternator. There is also an inefficiency in the whole system. We are converting mechanical energy, to electrical energy, to mechanical again to run the fan. This very inefficient, much less then just driving the fan directly via the mechanical energy of the rotating shaft.
We can see that the electric fan is a large current draw. The (gen 2) \'86-\'88 alternator is rated at 70A, and the 89+ unit is rated at 90A. Real world tests have shown that actual output is somewhat less then the specifications would indicate. Add the load of the electric fan, and you are that much closer to overloading an already factory-stressed electrical system.
While on this subject of the electrical system, look at how the fan is actually connected. The proper way to control an electric fan is via a thermostat and relay combination (fused, of course). Unfortunately, very few people actually do this. Many installations simply connect the fan to run all the time, or to a switch inside the car. In the latter case, your brain actually becomes the thermostat. This is a very poor arrangement as it is easy forget to switch on the fan as the temperature climbs.( I have been guilty)
Worse still, the 1989+ temperature gauge is inaccurate. By the time you see it move, the car is already too hot. Leaving the fan on all the time presents a different set of problems. It becomes an unnecessary drain on the system.
Lastly, there is the question of reliability. The stock clutch fan can have two failure modes:1. the clutch will fail, or 2. the fan will physically break.
The electric fan introduces many more failure points: 1. fuse, 2. all wiring connections, 3. physical failure of the fan, 4. failure of the motor, 5.failure of the thermostat.
It\'s not all doom and gloom for the Electric Fan........ some good points can be had....
Since you are no longer tied to the shaft of the water pump, the electric fan can be oriented in any way, and moved around to make space. Without the stock fan shroud in the way, there is much more room in the engine bay, as well as room to route things like intercooler piping, cold air intakes, etc.
An electric fan may also be required when going to certain aftermarket radiators that do not have provision for mounting the stock fan shroud.
Electric fans installs are also cheaper if your original clutch fan gets busted as new clutch fans are very costly, £279+ from Mazda compared to £160. for pair of elec fans with thermostats etc. Unless you get used stuff, then the goal post are moved...
T
he electric fan can also be left on after the engine is shut off. This allows continuous cooling to minimize heat soak. A small turbo timer like device can be used to run the fan for a preset amount of time.
So basically you have more controll over the cooling with an Electric fan set up......
Right there you go........ Electric fans are good but it all depends on what you want to gain from your machine!
Regards
:guinness
An electric fan is cheaper than a new hydrostatic fan :)
I agree with what you\'ve said, its worth noting that when the hydro static clutch goes tits it will either run the whole time or not at all. If its running the whole time you will notice your belt wear going up considerably.
I mounted my fan inside a frame, inside the origional radiator cowling and havve never noticed a heat buildup at idle. Its thermostat is set for 82deg.
With electric fan you will only have load on the alternator when the fan is on... obviously, this means that most of the time, you havent got the load, but as rotary engine dont have that much low end torque, the lectric fan gives you a little quicker pick up making it the equivilent of having a lighter flywheel.
I wouldnt leave it on all the time, got to have a thermostat and a light in the and an overid switch in the car. For when you are sitting in the queue at the Pod.:D
Question.............
Does the FD have electric fans because they are better and more efficient or because the rad is that stupid place and they had no room for the viscous fan
Hmmm, good question........
Using this {quote} The truth is that no one actually knows the CFM rating of the stock fan.
It has simply never been measured by anyone but Mazda/or specific car type manufacture. {Quote}
So maybe they know more on this, but seeing an FD\'s engine room space..... \'Dam\', it\'s like a camels arse in a sand storm!
Good question.......... :confused:
TBH it was probably done for the sake of reliability and cheapness, not to mention the space saving......
and weight, the TII fan weighs loads, just about everything on a TII is more substantial and metal compared to the FD which is plastic, even the oil filler neck is plastic on a FD compared to the metal one on a FC.