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DaleClark's all about fan control and the fan system

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Old 05-29-10, 04:39 PM
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OK guys,

Been meaning to put this all in one place for a while. Most of this stuff I've written in bits and pieces in other posts over and over, time to put it all in one place.

The FD has a pair of very good cooling fans to keep temps in check. If they are set up and run properly, you'll have a nice, cool running FD. If not, you'll be having problems.

First, a little about the stock fan system.

Fan System Components

- The fans. There are a pair of them (obviously) mounted to the radiator. They are 3 speed fans, there is a resistor built into the fans that drops the input voltage down to change the speed. Both fans always turn at the same speed and they are NOT independant - this is a common misconception. Just think of them as one unit.

- Fan speeds. There are 3 speeds, as stated - Low, Medium, and High. Again, think of the fans as a unit, if they're on low speed, they both turn at low speed, etc.

- Fan speed inputs. This is one area where people get confused. Each input adds up to the fan speed. If you only have 1 fan speed input active (more in a bit on this) you'll get Low. 2 inputs, Medium, 3 inputs, High. It doesn't matter WHICH input, each input in independent.

- Fan relays. These are the 4 relays on the bracket on the passenger side (right side) shock tower. The fan speed inputs trip the relays which send high amp 12v to the fans.

- Fan thermoswitch. This is the coolant temp sensor on the back of the water pump housing under the ECU coolant sensor. It has a one wire connector. This is one of the fan speed inputs. The factory switch operates at 107 deg. Celsius.

- The AC. Whenever the AC button on the dash is pushed on and the AC fans (not the radiator fans) are switched on, this is a fan speed input. Even if the AC doesn't work or is removed, this is an input.

- The ECU. The factory ECU can read the engine's coolant temps from the coolant temp sensor on the back of the water pump housing (the 2-wire sensor with a green plug on the back of the water pump housing). It uses this input as another fan speed input.

- The Electrical Load (ELD) system. The ELD module, which is mounted up above the ECU, receives inputs from various electrical devices on the car (defroster, headlights, etc.) and triggers an output to let the ECU idle up. It is also tapped into the same wire as the fan thermoswitch and can kick the fans up as a fan input.

How the system works stock and the Fan Recall


Stock the fans will not come on until 105 deg. C - this is when the ECU's fan input kicks in. At 107 deg. C the fan thermoswitch kicks on, giving another fan input. Anytime the AC is on, you get a fan input, and when the ELD is triggered by headlights or the like you get another input.

Now, 105 deg. C is HOT. Mazda ran the FD this hot for two reasons - emissions and fuel economy. A hot engine handles emissions better and is more fuel efficient. This was not the best decision from an engineering standpoint, but without it they couldn't have sold the car in the US. That's fine, we can do something about this.

When the FD was still young, Mazda had troubles with the FD running hot and causing engine fires. This was Not Good, so they issued a number of recalls and parts improvements related to this problem. One of the biggies was the Fan Recall. This has 2 components -

- A harness and control box that plugs in by the ECU. The harness goes in between the blue and white connectors to the ECU harness, has a ground wire, and a control box that bolts behind the ECU.

- A harness that plugs in between the fan relays and the front wiring harness. This changes how the relays are wired so they can kick on with the ignition key Off.

The fan recall harness worked by monitoring the fan thermoswitch. If the thermoswitch trips for a certain amount of time while you're driving (I believe 5 minutes or something) it will then remember that it was hot for that length of time and will run the fans for 10 minutes after the car has shut off to cool the engine bay.

While this extra cooling sounds good, remember this was in a VERY hot engine bay with a precat and 100+ degree coolant temps. This was quite hard on the battery and early FD owners reported batteries not lasting terribly long due to the recall.

How to make your fan system better

So, we want to get coolant temps consistently running where they should be and make the fan system happy. This isn't too hard to do.

First, pull the fan recall business. You won't need it. In an FD running SANE coolant temps and with a downpipe instead of a precat, the underhood temps will be nowhere near a stock FD's.

Next, get an FC thermoswitch. This is from the '89-91 RX-7, Ray at Malloy can get you one easily for around $50. It's the exact same as the FD thermoswitch (screws right in, uses the same connector) but kicks on at 97 deg. C which is far more reasonable.

Third, get a PowerFC if you don't have one already. Not only is the PFC one of the best things you can do for an FD, but you can control the ECU's fan speed input. You WILL need a Datalogit to change this. Most guys set it to 85 deg. C which is very comfortable. Mind, the Datalogit shows multiple fan "on" temps - only the first one works on the 93-95 PowerFC, the later ECU's had more fan outputs.

Fourth, if you want to get more hardcore, see if you can find an HKS fan controller. I'm not sure if they're made any more, I have one in my car. It gives full control over 2 fan inputs, I have mine set at 85 deg C and 90 deg. C. The unit is in the same case as their turbo timer, it's easy to wire in and set up, basically set it and forget it. Few FD guys have this, but I really dig it.

To reiterate, you have 4 fan speed inputs - AC, thermoswitch, ECU, and ELD. Each input brings the fan up one speed level. If you are running at 80 deg C and have the AC on, the fans will run at Low. When you hit 85 deg. C with your PowerFC and the AC still on, the fans kick up to Medium. When you hit 97 deg. C with the same 2 inputs active, the thermoswitch kicks on and you have the fans at High.

Could you run the fans at High all the time? Sure. The car will take forever to warm up and use more fuel, the alternator will be loaded down running the fans, and the life of the fan motors will likely be reduced. Your car will also sound like a giant fan all the time. That's a ghetto way to do it, use the fan control system to your advantage.

Can you run an aftermarket fan? Not recommended. Most aftermarket electric fans are pretty lousy - ask any FC guy. They typically don't move as much air, are MUCH louder, draw more amps, and fail prematurely. Mazda really did a nice job on the stock fans and I've yet to see an alternative that's any better. The only drawback to the stock fans are the size, they are a little bulky with some custom setups, but that's about it. They can move a LOT of air.

What about the '99 spec fans? Mazda redesigned the fans in '99 with different fan blades and motors that use less amperage. I've not seen conclusive evidence that they're better than the original fans, but please chime in if you have first hand evidence.

What fails in the fan system? It's generally pretty robust. I have seen bad fan relays before, that's an easy fix. The fans themselves are very hardy, I have seen ones damaged by battery acid and foreign object damage. The wire to the fan thermoswitch connector can break off, causing the thermoswitch to do nothing.

What about the fan switch mod? This is an oldschool mod from back in the day. Before the upgraded fan thermoswitch was discovered and altering fan temps in the PFC was hit upon, FD guys didn't really have a good way to run the fans and keep things cool. The fan switch mod taps into the ECU fan recall harness, you can ground that out to run the fans (it's the same wire as the fan thermoswitch) and then the fans will run after you shut the car off. This is simply not necessary with fans running properly.

That's about it. If you get your fans working for YOU, your FD will run cool and comfortable. Aftermarket radiators, big intercoolers, ducting, etc. are all useless if the fans aren't running like they should be.
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Old 05-29-10, 06:19 PM
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Dale, great write-up!

On mine I have a switch that if it turned on 2 minutes before shut-down it will cause the fans to do the cool down run.

I looked for my old info on that mod but haven't located it yet. I only use it on hot days when popping the hood is not an option.

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Old 05-29-10, 06:45 PM
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Dale excelent write up. Thank you for taking the time to write all of this down and share it with us. Epecially the part about the three inputs.


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Old 05-29-10, 06:49 PM
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Dale Clark, you sir, are a rotary Force of Nature... that was a excellent contribution to our FD knowledge base!
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Old 05-29-10, 07:04 PM
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Edit: Never mind. The HKS Fan Controller has, in fact, been discontinued.
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Old 05-29-10, 07:16 PM
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Originally Posted by Barry Bordes View Post
Dale, great write-up!

On mine I have a switch that if it turned on 2 minutes before shut-down it will cause the fans to do the cool down run.

I looked for my old info on that mod but haven't located it yet. I only use it on hot days when popping the hood is not an option.

Barry
my old FD has a turbo timer, so you shut the engine off, turn the key back on, turn the AC on, and then let the turbo timer run the fans....

i think it worked too, engine is original, 118K, turbos have never been off, paper intake gasket even...
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Old 05-29-10, 09:32 PM
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Originally Posted by DaleClark View Post
First, pull the fan recall business

By this you mean the black control box by the ecu?
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Old 05-29-10, 11:25 PM
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Dale, fantastic write up. I love this kind of writing which I learn more and more about the car.

what is your thought about the pettit fan switch mod? does it run high all the time?

if I add a small fan for intercooler, where do you recommend to hook to?

thanks
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Old 05-30-10, 12:00 AM
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Great write up Dale. I know you said you don't recommend aftermarket fans, but I heard that fle-a-lite make a dual fan that works very well for the fd. The fans are a little wider, but heard they are better that the stock. Have you had or anyone else had any experience with this fan set-up. Thanks Justin
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Old 05-30-10, 12:46 AM
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As others have said, thanks for taking the time. I "sort of" knew how things worked, but this clarified a few things.

It's also nice to hear someone of authority confirm what I always felt....that the stock fans and shroud were NOT a weak point in the cooling system. Seems like alot of owners want to fix something that isn't broken.

That said, what are your thoughts on the "upgraded" OEM fan blades? IIRC, the ones that add a blade to each side? Haven't checked lately, but I think MazdaMotorsports sold them. Any real benefit?
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Old 05-30-10, 12:58 AM
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Good writeup. Dale and I agree to disagree on the fan recall (aftercool system to run the fans after engine shuts off). I see value in it for many setups. Mazda is still using aftercooling on the Rx-8. The fans turn on at 97C on the Rx-8 (if A/C is off). On the 09+ models the aftercool comes on based on an engine bay temperature sensor.
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Old 05-30-10, 09:23 AM
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Funny, on monday I was just toggling my A/C switch (even though my A/C has been removed since like 2000) while on the road race track to kick my fans into high gear

I also use my turbo timer primarily to run my fans on high for about 5-6 minutes after shutdown (don't use the timer much with the car on). I have a battery tender junior that keeps my battery charged so that all that running of fans doesnt kill it.

Dale, thanks for taking the time to write all this up

P.S. Has anyone had their fan motors fail? I'm wondering about their life expectancy, they're getting up there in years and mileage of use, and brand new they're retarded expensive.
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Old 05-30-10, 11:22 AM
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Originally Posted by arghx View Post
Good writeup. Dale and I agree to disagree on the fan recall (aftercool system to run the fans after engine shuts off). I see value in it for many setups.....
I agree. Nice writeup; however, I see no need to remove the fan [recall] mod. (fan mod is the black box and a couple of wiring harnesses)

Originally Posted by GoodfellaFD3S View Post
.....P.S. Has anyone had their fan motors fail? I'm wondering about their life expectancy, they're getting up there in years and mileage of use, and brand new they're retarded expensive.
Yes. I had one start to seize up after about 200,000 miles--it was making a whining sound. I was able to carefully disassemble it and grease the bearings. It was otherwise in good shape; the motor is very robust and should be good for another 15 years.

It's been back in service for about a year and working fine. I did both of them while I had things apart.
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Old 05-30-10, 12:38 PM
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Wow, buncha questions. First off, thanks for the good words. I figure that the more of this stuff that's written up the more Mahjik can point noobs to one of my posts .

There's some disagreement on the value of the fan recall system. I think it just really doesn't have much merit in everyday driving. After a real hard run or track duty, a cooldown is a good idea, but in that case I think it's smarter to let the car idle with the hood up for a while - that will really cool things down. Rich's turbo timer idea has merit too.

I believe the FD can be a "regular" car, not something that needs special tricks and procedures for everyday use. When I take my car out, I hop in, start it, and go. When I come home, I pull in the garage, turn it off, and go in. No letting the car warm up in the driveway, no popping the hood in the garage to cool it off, etc.

One of the best things you can do for underhood heat is get a downpipe and get it ceramic coated. This makes a massive difference in underhood temps. Soon after I bought my car (probably around 68,000 miles) I put on a Jet-Hot 2000 coated downpipe. My wiring harness is still soft and good, popping the hood doesn't create a huge wave of heat, etc. with 114,000 miles on it, many of those miles driving my car FOR work on service calls in Florida heat with the AC going.

Another thing I don't like with the fan recall harness is how sloppily designed the harness is. The underhood harness is way too long and makes a big hot mess of wires by the relay, the ECU harness is also a big sloppy mess.

BTW, the '95s had the recall harness built into the wiring harnesses, and if you have a newer ECU harness the fan recall ECU-side harness is built in as well. Not sure if JDM cars ever had a fan recall or if they installed this system on JDM cars.

I do have a set of the later fans in the attic, but JUST the fans. The holes in the middle of the fans are larger than the shafts on the earlier fan motors. Some people have built up the shafts so they're the same size. I'm still wanting to do this at some point but it's a back burner project. I'd really like to get the full deal with the later motors and everything.

Aftermarket fans - I'm just still not a fan of them. Most aftermarket fans are single speed and the wiring and relays that come with them are substandard quality. Seems like in the domestic world they just put up with substandard parts, especially with electronics. I want Japanese OEM quality, 200,000 mile quality. With something as important as the cooling system, you don't want to risk it with cheap or crappy parts.

The fans can move enough air to do the job, most cooling problems are moreso the result of a crappy radiator, bad ducting, or general cooling system problems (thermostats, air in the system, etc.).

Dale
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Old 05-30-10, 03:19 PM
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Very nice writeup.

IMHO, running the fans when the engine is off will not do a very good job of cooling down the engine. Without the water pump spinning, the coolant in the radiator gets cool but the coolant inside the engine stays warm (usually gets hotter due to lack of coolant flow). Anyone with an aftermarket water temp gauge should be able to check this for themselves... turn the key back on after a couple of minutes and observe the water temp, then start the engine and let it run for about 30 seconds and watch how the coolant temps drop.

I suppose there may be some benefit in removing some hot air from the engine bay, but I suspect a better solution would be to open the hood (or install a vented hood) if you are concerned with engine bay temperatures. Personally, I don't like the additional drain on my tiny aftermarket battery.

Last edited by scotty305; 05-30-10 at 03:21 PM.
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Old 05-30-10, 03:27 PM
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thanks Dale good job!
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Old 05-30-10, 03:44 PM
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Originally Posted by scotty305 View Post
Very nice writeup.

IMHO, running the fans when the engine is off will not do a very good job of cooling down the engine. Without the water pump spinning, the coolant in the radiator gets cool but the coolant inside the engine stays warm (usually gets hotter due to lack of coolant flow). Anyone with an aftermarket water temp gauge should be able to check this for themselves... turn the key back on after a couple of minutes and observe the water temp, then start the engine and let it run for about 30 seconds and watch how the coolant temps drop.

I suppose there may be some benefit in removing some hot air from the engine bay, but I suspect a better solution would be to open the hood (or install a vented hood) if you are concerned with engine bay temperatures. Personally, I don't like the additional drain on my tiny aftermarket battery.
+1. confirm! I did see what you're talking about. plus when I have the fans on after engine off, the idle is pretty rough on the next start. it seems like PFC do the idle learning all over again.
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Old 05-30-10, 09:58 PM
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Thanks Dale. Very well written!

Couple of questions -

you suggest getting an FC thermoswitch because of the lower set point, but if I am running a PowerFC can I accomplish the same thing by telling it to turn the fans on at a lower temperature?

I removed the short fan relay recall harness when I first got my car running. Would go out into the garage and find the fans running with the ignition off for no reason. I assumed I had a problem with the little black box but never pursued it. Sounds though, from your writeup, that I really won't miss much without the recall. Do you agree or should I try to troubleshoot it?

Jeff
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Old 05-31-10, 12:40 AM
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As stated, the ECU (and the PowerFC) only has control over 1 fan speed input, that's it. The FC thermoswitch drops that fan input from 107 deg. C to 97 deg. C which is a great idea. The FC thermoswitch should be in every FD.

With the fans running for no good reason, I'd just ditch the fan recall crap. That would make that situation an impossibility.

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Old 05-31-10, 11:35 AM
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Originally Posted by DaleClark View Post
I'd just ditch the fan recall crap. That would make that situation an impossibility.

Dale
By that you mean the small black box by the ecu???
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Old 05-31-10, 12:07 PM
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All I did was remove the recall harness at the relays. Fan connectors plug directly into the relays. That stopped the fans from coming on for no reason.
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Old 05-31-10, 01:45 PM
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FWIW, attached are a schematic of the recall fan mod, and a "coolant table."
Attached Thumbnails DaleClark's all about fan control and the fan system-cool.-fan-mod-schematic.jpg   DaleClark's all about fan control and the fan system-coolant-fan-control-table.jpg  
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Old 05-31-10, 06:49 PM
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Originally Posted by DaleClark View Post
The FC thermoswitch should be in every FD.
This is a point I have also made many times. Once you understand the 3 speed control system it makes sense why adjusting the PFC fan trigger isn't "the same thing" as getting an FC thermoswitch.



I had my own little thread about cooling fan stuff, it was a more picture intensive technical description of how the system worked rather than the guide format of this thread. https://www.rx7club.com/3rd-generation-specific-1993-2002-16/why-engine-so-damn-complicated-part-3-cooling-fan-controls-876767/
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Old 05-31-10, 06:56 PM
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IMHO, running the fans when the engine is off will not do a very good job of cooling down the engine.
Try manually running the fans after the engine has shut off on a hot day. Watch the temperature gauge and you will notice that the temps will not spike anywhere near as much.
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Old 05-31-10, 07:34 PM
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Dale, not sure if appropriate for this threaad, but I believe it goes hand in hand with your cooling fan recommendations. If not, please delete. Since you recommend the Apexi PFC and the A/C is one of the cooling fan inputs, we might want the A/C fan/compressor fix in the same thread. Bottom line, for most FD owners with PFC, the A/C compressor only comes on when the fan switch is in one or two of the four fan speed positions. The fix below is the only one I know of that absolutely fixes the problem once and for all.

The best fix is from Freddie Hebert.
Category Five Motorsports
Power-FC A/C MOD

This mod will enable your air conditioner to work when installing a Power FC in FD3s. This will also fix the problem of the a/c not working on one or more of the fan speeds.

The reason the a/c does not come on is because as the car ages, the ground signal going to the ECU’s (wire 1E) is receiving a fuzzy ground signal. Some cars have no problem with the signal, but some do; the last FD I worked on the a/c did not work on any speed. This mod will interrupt the signal going into the Power FC and redirect it through a simple Bosch relay. This will also let the Power FC still control the ISC and switch the a/c off at wide open throttle.

Locate wire 1E (Violet wire) - it is the third wire from the end on connector one. Cut the wire 2” from ECU. On the harness side you will hook 1E to (86). On terminal (85) on the relay will go to ignition +. Terminal (87) will go to 1E that was cut on the Power FC side. Terminal (30) will go straight to chassis ground. Now when your a/c is turned on, it will receive a nice healthy ground. If you have any questions contact me via email.

[email protected]
(note: I don't know if this address is still good. It is from an old thread)
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