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Old June 3rd, 2010, 15:49
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ehall ehall is offline
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simple dual-electric fan setup

This is the electric fan setup I've been using on my beater project for a while. I've recently been able to test it in 90-plus degree weather, and it seems to work pretty reliably, so I feel comfortable writing about it now. The basic idea is to use the stock XJ fan "layout" on the radiator, but using an electric fan in lieu of the mechanical fan. This means putting a single electric fan inside the mechanical fan's shroud, with an independent temperature switch turning the fan on and off as needed. The stock condenser fan is also still present, but it is still under the control of the ECM and isn't involved in the normal cooling. It's possible to go beyond this setup with a manual override switch or a fan controller or whatever, but I haven't done any of that for now.

The first step is to eliminate the mechanical fan assembly and make room for an electric fan motor. Some people chop the nub off the accessory bracket with a sawzall, but I replaced my accessory bracket with one from a YJ, which got rid of the fan nub and also moved the alternator five inches higher (see here).

Next is the fan itself. I spent a lot of time looking at options and eventually settled on the left-side fan from a 3rd or 4th generation Ford Taurus. Most of the Taurus fan swaps are for the single big fan from a 3.8L engine, but the 3rd and 4th gen engines use two fans next to each other, and this mod uses the left-hand fan from those setups since it is a little larger. Specifically the left-side fan is approximately 14.5" outside diameter, while the opening in the stock mechanical fan shroud is approximately 15.5" inside diameter. This lets the fan drop into the stock shroud with only some minor modifications. Here is a pic showing the fan sitting in the shroud before any modifications



In order to make the fan fit into the shroud, I chopped off the excess plastic parts and trimmed the outside edge so that it would fit cleanly. Then I used 1/4" stainless steel carriage bolts, spacers, and nylon lock nuts to secure the fan into the center of the shroud.





Test for fitment and make sure nothing interferes. You can see from the pic below why the mechanical fan nub has to be removed first



Now for the electronics. These fans have two positive wires and one ground, but there is only one winding on the motor. The way these are wired up in the 3rd gen Taurus is that one of the power wires goes through an inline resistor that kicks the voltage down, which provides a "low speed" operation, while the other wire goes straight through and provides a "high speed" operation (which is really the "normal" speed). You can do this too if you want, however for the purpose of this write-up I am just doing a single unmolested input that will turn the fan on and off according to temperature.

I tried a bunch of switches (over $100 in rejects) and the most consistent and reliable thing I've found so far is a two-pin switch from late-80s/early-90s BMW models (Four Seasons part number is 36511, the one I bought from NAPA was ATM part number 1435033). According to the specs, it is supposed to come on at 95c (203f) and go off again at 90c (194f) which means it should only come on after thermostat is fully open and go off again when the thermostat is starting to close.

Unfortunately the switch uses an M14x1.5 thread, so it will not fit into any of the stock openings. You might be able to drill and tap a hole in the front of the thermostat housing for this, but I already have a gauge sender there so I had to use something else. I also tried drilling and threading a 3/8 NPT to 1/4 NPT adapter bung but the sidewall of the bung ended up being too thin and would crack after a few heat cycles. The thing that finally worked for me was a 4" long 1.25" OD brass pipe nipple installed in the upper radiator hose. I drilled a 1/2" hole and then used a M14x1.5 fine-pitch stainless steel bolt to make a thread in the pipe (a tap would work better but I couldn't justify the $40 for a single use tap). Brass was soft enough for this, and was thinner than the galvanized or plastic pipe. If you go this route make sure the pipe is long enough to chop the threads off the end, since pressurized coolant will travel up the threads and try to leak out. Here's a pic of the switch installed.



From there it's just a simple relay to turn the fan on and off. Since everything is by the battery this is pretty simple to setup. In my case I chose to run constant battery power to the switch and fan, then run the ground leg for the switch to the relay, since this is similar to how the stock fan operates, and should be easy to wire up an override switch (short to ground basically). Here's a pic from the rear, using an earlier test switch. You can see the relay on the fender wall.



One artifact of using constant battery power is that the fan will run after the engine cuts off if the switch is closed. This happens almost everytime I drive the jeep, but the temperature of the coolant at the switch is knocked down pretty quick so the fan does not run very long. Actually it will cycle a few times as the hose heats up from the coolant that's still in the engine, then it cools off, heats up again, etc. I've never had any problems with battery draining or anything, but if you want to feel more comfortable you can tie the switch into ignition power from the PDC if you prefer.

Another option worth looking into is a three-pin switch for the same generation of BMW vehicles, which provides two independent switches at 194f and 207f respectively. In conjunction with the 3rd gen Taurus inline resistor, this could be used to drive the "low-speed" and "full-speed" pins on the fan motor as well.

Anyway in the past few months of testing I've been very pleased with the fan, and the setup has performed pretty much the same as the old mechanical setup did. Driving down the highway the gauge is below the 210 hash mark, but when I stop at a red light or a drive-through window the gauge starts to creep into the 210 hash mark, and then the fan kicks on. Once I start moving again (or if the outside temp is cool enough for the fan to do the work alone) the temp will drop to below 200 and the fan will go off. There has only been one time where the secondary fan kicked on due to ECM command, and as expected the temperature dropped very quickly with both fans spinning.

Overall very glad I made this modification as it gives me more control, and eliminating the mech fan also eliminated a noticeable amount of drag on the serp belt.

Here is the final parts list for my installation

stock mechanical fan shroud
left-side 3rd or 4th generation Taurus fan (3.0L)
four 1/4" carriage bolts, lock nuts, and misc spacers
two-pin BMW fan switch (Four Seasons 36511, or NAPA ATM-1435033)
one relay
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Last edited by ehall; June 3rd, 2010 at 15:59.
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  #2  
Old June 3rd, 2010, 19:44
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Hellbent Hellbent is offline
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Re: simple dual-electric fan setup

cool. at some point i will be converting to a dual electric fan set up, something along these lines.
how would you rate the airflow of the taurus fan against the stock xj fan? and is your stock electric the older or newer style(10 blade) fan?
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Old June 3rd, 2010, 19:47
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ehall ehall is offline
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Re: simple dual-electric fan setup

I don't know about CFM but it puts out a LOT of air, can really feel it on my hand

My aux is the old six-square style. I've been looking to get a 10-curved style but haven't found one for what I want to pay
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Old June 3rd, 2010, 21:04
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DeftwillP DeftwillP is offline
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Re: simple dual-electric fan setup

So final items price list?
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Old June 3rd, 2010, 21:17
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ehall ehall is offline
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Re: simple dual-electric fan setup

$40 for the junkyard fan, $20 for the switch at NAPA, a couple of bucks for the hardware, and I had the other stuff already
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Old June 3rd, 2010, 22:28
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austinaubinoe austinaubinoe is offline
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Re: simple dual-electric fan setup

Thats the simplest write up I have ever seen! thanks alot for it!

i dont really get how you tapped the pipe though, how does that hold?
What kind of relay is it? part#?

That seems a little steep for a junkyard rad fan. I mean, how many people want those??

Might do this this weekend, you left the stock clutch/belt right? just removed the fan blades?
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Old June 4th, 2010, 06:58
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ehall ehall is offline
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Re: simple dual-electric fan setup

Quote:
Originally Posted by austinaubinoe View Post
i dont really get how you tapped the pipe though, how does that hold?
I would have used a tap if I'd had one. Actually the local garage I use has a set of taps and they would have done it for a couple of bucks, but I had the bolt so I used that instead. Since stainless steel is much harder than either brass or aluminum (even grade-5 steel, or class-8.8 in this case), it will cut a thread pretty easily if you go slowly. The hardest part is keeping the bolt square and level while getting the thread started, since it will go off-kilter pretty easily. One thing that helps cut a couple of slots down the bolt lengthwise, which makes it act more like a tap and less like a bolt. Here's a pic, cut a couple of slots like that and it works like a tap for the soft metal.



The wall thickness of the brass is about 1/8" but since the pipe has a curve the total engagement is more than that (sides engage the threads lower than the center). I did use some thread sealant to help reduce leaks, but the switch also came with a little aluminum collar that also helps to make a seal (you can see the ring in the installation pic). You can find the pipe nipples in brass, PVC plastic, or galvanized steel. Brass is soft and had a thinner wall than the steel or plastic nipples. I would prefer to drill and tap the thermostat housing if possible (I don't know if the front has room for a 1/2" hole).



Quote:
What kind of relay is it? part#?
It's a standard 5-pin 30-amp relay. It's the same relay you've got all over your jeep. I think that one came with the Hella fog lights but I have bunches that I've grabbed from the junkyards.

Quote:
That seems a little steep for a junkyard rad fan. I mean, how many people want those??
Junkyards around here are stupid expensive about some things. Nominal price for a rear drive shaft is $125...

Quote:
Might do this this weekend, you left the stock clutch/belt right? just removed the fan blades?
No I replaced the whole accessory bracket, follow the link in the write-up
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Old June 4th, 2010, 07:37
O-Gauge Steamer O-Gauge Steamer is offline
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Re: simple dual-electric fan setup

Great write up. In the past I have wired the electric to run after engine shut down. It REALLY helps to eliminate heat soak. Not that we have any of that...
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Old June 4th, 2010, 09:59
fuzzydog fuzzydog is offline
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Re: simple dual-electric fan setup

Great write up - it will help me refine my setup.

I currently am running one of the large taurus fans. I originally had it hooked up to a Hayden temp controller which worked fine til it crapped the bed in about 6 months use. I did an emergency fix which has become semi-permanent - I have a relay for high and a relay for low connected to a 2 position switch in the dash. Down for low speed, up for high speed, off in the middle.

I just did some quick research and there is a 91 degree switch for this vintage of BMW (Standard part # TS288) and also the 3pin switch the OP refers to is Standard part #TS296.

I have a couple of sets of the dual taurus fans in my storage shed that I picked up at PNP, intending to change my single large to the dual small.

I think the ideal setup would be dual small Taurus fans hooked up to that 3 pin switch with the low temp turning on one of the fans, and the high temp turning them both on.

And the icing on the cake will be after cooling. My turbo 88 Audi (now sold ) had an electrical after run coolant pump which would circulate coolant through the engine, turbo and rad, with the fan running after the engine was shut down. It would do this until it reached a preset temp. Unfortunately the pumps on those Audi's are freakin expensive and used ones are generally very brittle due to their age and heat cycling.
But all is not lost because my current DD, a 1988 Mercedes benz 300 also has an aux electric coolant pump which seems less complex and more durable (and which I picked up a spare of from a wreck for dirt cheap). Just an interesting side note, while the electric coolant pump on the Audi was to cool the engine/turbo after shut down, the pump on the Benz is for earlier warming of the cabin - Before the tstat opens, it takes coolant from the engine and pumps it to the heater core. This is so that the inside of the car gets warmed up quicker in the cold months. I love those freakin Germans

So I am going to add a circuit to turn the fan on by the high temp switch with the engine shut off, which will also turn on the electric coolant pump to circulate the cooled coolant from the rad into the engine. I don't think it's really neccessary, but will be cool to do.
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Old June 4th, 2010, 16:54
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DieselSJ DieselSJ is offline
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Re: simple dual-electric fan setup

Nice setup. Instead of the copper/brass nipple, how about something like this for mounting the switch?

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Old June 5th, 2010, 21:59
joe_peters joe_peters is offline
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Re: simple dual-electric fan setup

Nicely done!
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Old June 11th, 2010, 11:20
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1990JEEPXJ 1990JEEPXJ is offline
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Re: simple dual-electric fan setup

is it necessary to modify the accessory bracket and all that like you did in your link, or can you just remove the mech fan, clutch and nub and still have the room?

and is yours wired so the high setting is the one to come on?
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Old June 11th, 2010, 12:00
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ehall ehall is offline
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Re: simple dual-electric fan setup

Quote:
Originally Posted by 1990JEEPXJ View Post
is it necessary to modify the accessory bracket and all that like you did in your link, or can you just remove the mech fan, clutch and nub and still have the room?
I don't know if the nub needs to be completely removed. The nub sticks out pretty far, and the electric fan can only go so far into the shroud, but you might be able to make it work.

Quote:
and is yours wired so the high setting is the one to come on?
Although there are two positive terminals on the fan, there's only one winding on the motor, so the same input voltage makes it spin the same speed regardless of the input pin that is used. With the 3rd generation Taurus, they use an in-line resistor on one of the wires to knock the voltage down to one of the pins (producing low-speed operation on that circuit), but that is the car wiring not the fan motor. FWIW the 4th gen uses the same fan but only has one circuit (the other pin is unwired), and the ECU uses PWM for speed control
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Last edited by ehall; June 11th, 2010 at 12:30.
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Old June 11th, 2010, 13:56
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sledneck sledneck is offline
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Re: simple dual-electric fan setup

I have close to the same setup but I routed one fan to stay on when the motor is running and put the other on a swith in the cab. I only have to turn the second one on when im going pretty slow on a trail.


I also did the washers and longer bolts on the rear hood mounts so the back of my hood has about a 1 inch gap. I havent overheated since I added the washers but its not supper hot here yet (about 80-85).
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Old June 11th, 2010, 14:42
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hubs97xj hubs97xj is offline
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Re: simple dual-electric fan setup

Out of curiosity, is the fan pn 5F1Z8C607B? If not, could you guys post up the numbers? A quick check says the replacement Taurus fans (just grabbed the 2000 3.0 DOHC numbers) and the wiring connector are cheaper than replacement Jeep 4.0 fans. My current setup is adequate, but could be improved, and I'd like to be able to just pop the shroud off in order to change fans out, which I can't do currently.

I'd also be interested in the max current draw of the Taurus fans if anyone has that info handy. I know the single Taurus setup draws more than my controller will handle, so something with lower amperage would definitely suit my needs better.
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