Controlling dual electric fans

[Roxtar]

I did a search on this and never got a defining answer. I just finished my conversion to dual 12" electric fans and I have a question about controlling them. I'm now running them both off a relay controlled by the stock aux fan connection. This kicks them both on whenever the temp gets above 220 and kicks it off at about 210. This keeps the temp above 210 constantly. I'd prefer to keep things a little lower by separating the two, running one as an aux like I currently do but having one kick in sooner (but not running full time from start up). I saw one mention of a GM fan control but nothing more on that. How do others control their electric fans?

[MuddinXJ]

you could get a temp guage and just hook the other fan up on a switch and then kick it on when you feel adequate.

[Roxtar]

you could get a temp guage and just hook the other fan up on a switch and then kick it on when you feel adequate.
I have a temp guage and thought about that. If fact, I will have a manual override switch but would rather not have to be always monitoring the temp myself since it is a DD.

[MuddinXJ]

well just mount the guage so when your driving you can just glance at it. thats what i do when im driving(although no fan mods yet).

[Bender]

I'm running dual electric fans with dual speeds,

I bought a newer style t-stat housing ($10 at dealer) that has the threaded hole for a sensor. I went to the parts store and looked through the sensor catalogue to find a temp switch that fit the hole, turned on around 212 and turned off around 205. I used that switch to initiate the "low" fan speed and used the stock temp switch in the rad to initiate the "high" fan speed.

Use double relays for each fan speed to ensure you don't overheat them.

[Roxtar]

I'm running dual electric fans with dual speeds,

I bought a newer style t-stat housing ($10 at dealer) that has the threaded hole for a sensor. I went to the parts store and looked through the sensor catalogue to find a temp switch that fit the hole, turned on around 212 and turned off around 205. I used that switch to initiate the "low" fan speed and used the stock temp switch in the rad to initiate the "high" fan speed.

Use double relays for each fan speed to ensure you don't overheat them.
I don't have a "stock temp switch" in the radiator that I'm aware of. I only have the sensor in the t-stat housing.
I should have added I have a '99.

[Bender]

Then you're on your own :D

[FELIX]

Wire a switch, for 1 or both of them, then you can control the fans to turn on when you want them to.

Rob

[BrettM]

I have my electric wired only manually and I just keep an eye on my guage. If you're going to hook it up to a sensor, why have one turn on at 210 and the other at 220? why would you ever want it getting to 220? Have them both turn on at 210, or maybe one at 205 and the other at 210.

[Roxtar]

I have my electric wired only manually and I just keep an eye on my guage. If you're going to hook it up to a sensor, why have one turn on at 210 and the other at 220? why would you ever want it getting to 220? Have them both turn on at 210, or maybe one at 205 and the other at 210.

I think you misunderstood my post. I agree with you, that's the problem. I don't want them to wait as long as they do to kick on. I'm looking for ideas on how to get them kicking in quicker and lowering the running temp. Possibly simillar to the OEM with one kicking on at 180 or so and one at 210. Basically trying to keep the temp in the 200-210 range.

Guys, I appreciate the help but I don't need to have the obvious stated. Perhaps I wasn't clear on my origional post. I know I can just use a switch, or hook them to an ignition hot to run constantly. What I'm looking for are some ideas on better ways to control when the fans automatically kick in.

[ZmOz]

Lots of places sell aftermarket thermostats for aftermarket fans. You can set the temps at whatever you want and just wire it up to your fans...

[Bender]

If you want to know why you'd want a fan to turn on at 220 ask the engineers at DC. That is what the aux fan was set to come on at in the early 4.0L's.

I don't see why you'd want a fan to come on at any temp lower than your desired operating temp. Considering the 4.0L's are made to run in the 200-210 range I would stick with the stock 195 degree t-stat and find a switch that comes on around 210 as they always require a variance in temp before they turn off. A switch coming on around 210 will probably go off around 202 which gives a little buffer of 7 degrees before the t-stat starts to close.

With your setup like that the fans would never be on at highways speeds...only during slow driving.

[Bloose]

Boy, lots of posts for such a simple problem with a simple solution. I personally am not a fan (pun intended) of having to turn the fan on myself. Leaving it run all the time is unnessasary and watching my temp gauge is just one more thing I have to do when I should be paying attention to the road or trail.

If you go to Summit Racings web site there are quite a few thermostats for controlling cooling fans. From a simple one that straps to the bottom of the upper hose, to fully adjustable ones. They are simple to install and made just for this task. I would get one, install and wire it to your primary fan, and forget about it.

Got to www.summitracing.com then click on shop on line, then cooling, and finally Fan Accesories. There is an adjustable unit on there from Perma cool for $24.

HTH,
B-loose

[Roxtar]

Boy, lots of posts for such a simple problem with a simple solution. I personally am not a fan (pun intended) of having to turn the fan on myself. Leaving it run all the time is unnessasary and watching my temp gauge is just one more thing I have to do when I should be paying attention to the road or trail.

If you go to Summit Racings web site there are quite a few thermostats for controlling cooling fans. From a simple one that straps to the bottom of the upper hose, to fully adjustable ones. They are simple to install and made just for this task. I would get one, install and wire it to your primary fan, and forget about it.

Got to www.summitracing.com then click on shop on line, then cooling, and finally Fan Accesories. There is an adjustable unit on there from Perma cool for $24.

HTH,
B-loose
Thanks, I have a couple questions. First, on the controls with the probe, do these fit in the hose or just in the radiator fins (on the outside). I've seen the fin type and don't like it since it's not in the water and I believe would not give a true temp reading. If they fit in the hose how do they seal?
Second, I like the fan switch type that would screw in to the factory aux fan sensor location but would those work with my computer? Doesn't the OEM sensor also suply the computer with the temp info so it knows to adjust the fuel mixture?

[Bloose]

Yes the probe type goes in the fins of the radiator. The fact that it doesn't touch the water is no problem as it is adjustable. If the probe temp is 180 when the water temp is 195 that relationship will likely always be very close to the same. This is actually the setup I would recommend over all others just for the adjustability. As far as the hose type that straps to the bottom of the hose and is not exposed to the coolant either. The type that screws into a boss would have to be used in addition to any factory sensors. So you would have to either find an unused threaded hole (as close to or in the t-stat housing) or introduce one into the system. As I said the probe type is likely your best option. I would order it from Summit. If you don't like the way it works they'll take it back within 30 days. You would just be out the shipping. But I really think you'll find it to your liking.

HTH,
B-loose

[Roxtar]

Yes the probe type goes in the fins of the radiator. The fact that it doesn't touch the water is no problem as it is adjustable. If the probe temp is 180 when the water temp is 195 that relationship will likely always be very close to the same. This is actually the setup I would recommend over all others just for the adjustability. As far as the hose type that straps to the bottom of the hose and is not exposed to the coolant either. The type that screws into a boss would have to be used in addition to any factory sensors. So you would have to either find an unused threaded hole (as close to or in the t-stat housing) or introduce one into the system. As I said the probe type is likely your best option. I would order it from Summit. If you don't like the way it works they'll take it back within 30 days. You would just be out the shipping. But I really think you'll find it to your liking.

HTH,
B-loose
I'm still concerned about having the probe outside. I live in the midwest and it would seem that outside temperature (100 in August, -10 in February) would effect it but maybe it is my best shot.

[Bloose]

I think it would work just fine. But that just my opinion. If the fins are cool relitive to the water they will disapate much more heat and it is likely the fan will not be needed. If you put the probe nerest to the water inlet for the upper hose I doubt you will have any problem at all. I to live in the Midwest and this is the system I would use. As a matter of fact it is the system I will be using on my 1968 Ford, though that is never driven in the winter.

Like I said for $25 I see no reason at all not to try it.

B-loose

[Clean Racing]

Ok If you want to control the fans seperatley... I would go with something a little more complex. There is a kit that I have used on street rods to control the fans electronically. I have only been able to find it online at speedway motors in nebraska.

http://www.speedwaymotors.com/
go to street rod products, then the heating cooling section page 3 you should find some cool stuff there. The electronic controler is what I have on order for my xj, since I am removing the clutch fan and replacing it with a 2000 aux fan.

[Dr. Dyno]

I tricked the engine's computer to switch on my dual electric fans at 210* instead of 220* by splicing a 4Kohm resistor across the two wires going into the coolant temp. sensor (CTS) in the t'stat housing. I even added an on/off switch to disable the parallel resistor circuit in the colder months. Here's my write-up:

http://www.angelfire.com/my/fan/CTS.html

I really only recommend this mod if you live in a warm climate and have a 180* or lower t'stat.
The output from the CTS also affects the A/F mixture during cold starting and warm up so my resistor trick does have a couple of minor side effects. It causes the engine to run leaner during this period and switch into closed loop operation at a lower temp. (130*F instead of 165*F) You'll find that the engine cranks over a bit longer on a cold start and the idle speed will be lower (~800rpm instead of 1100rpm) during the warm up phase. This isn't a problem as long as the ambient temp. is above 70*F.

[seanR]

Kid, I had one of those "probe" type t-stats. I but the probe in to the top rad hose, Just bend the wire into an 's' and run it between the t-stat housing and the hose. I used two clamps on the hose to keep it from leaking. Make sure you get a good quality adj t-stat and run it through a relay or you will burn out the adj. t-stat.

[Eagle]

I posted in your parallel thread on OEM that I don't like Dr. Dyno's method of tricking the ECM. On the '99 the same temp sensor serves the aux fan and the injection/ignition. Data goes into the ECM and the ECM controls the fan. Dr. Dyno's XJ, based on comments in other threads, is not U.S. spec and thus what worked for him may not work on a U.S. spec vehicle, especially not a '99 with OBD-II.

Okay -- here's a simple solution. The old Renix non-HOs ('87 - '90) used a simple switch in the radiator tank to control the fan. How about taking your radiator to a shop and have them solder in a threaded bung to accept one of those switches? Wire from that switch to a relay for each fan and you're done. I believe the temp setting for that switch is 217 degrees, although my '88 FSM says 190.

[Bender]

Eagle,

The descripency in temp's is probably due to the location of the switch. The switch could be seeing 190* on the cool side of the rad while the temp at the engine temp sensor it closer to 217*.

[8Mud]

To take Eagles idea one farther, the temp. switch, stock size, comes in various temps. Same switch, same threads, different values. I found my 210 replacement at the junk yard one day (in a Renault I think). I´m sure the right manual, at the autoparts store, has the information on the temp. values, all you have to do is match the thread size (and somewhat the depth).
On my mud truck, I have dual electric fans, soldered the bung (thread part) onto the radiator, cleaned the copper good and filled the cavity with heat conductive paste. The switch doesn´t have to be in the coolant flow, just needs a very good contact with the copper, the temp. difference between the copper and the coolant is minimal.
Just as an experiment, I tried soldering a temp. switch directly to a radiator, no go, 600F or so was too hot for it. My next attempt, will be a heat conductive epoxy and glue that sucker on there.
I have a few broad range, sensitive electronic thermometers, kind of interesting doing temp. readings on different parts of the motor and various locations in the coolant flow.

[Roxtar]

Okay -- here's a simple solution. The old Renix non-HOs ('87 - '90) used a simple switch in the radiator tank to control the fan. How about taking your radiator to a shop and have them solder in a threaded bung to accept one of those switches? Wire from that switch to a relay for each fan and you're done. I believe the temp setting for that switch is 217 degrees, although my '88 FSM says 190.
I like the idea of soldering the threaded piece into the radiator. That may be the way to go. I just called a radiator shop who quoted me $30 for that.

[Dr. Dyno]

I posted in your parallel thread on OEM that I don't like Dr. Dyno's method of tricking the ECM. On the '99 the same temp sensor serves the aux fan and the injection/ignition. Data goes into the ECM and the ECM controls the fan. Dr. Dyno's XJ, based on comments in other threads, is not U.S. spec and thus what worked for him may not work on a U.S. spec vehicle, especially not a '99 with OBD-II.

My '92 XJ indeed isn't US spec but the only difference in my electronic control from the US spec is a lack of an O2 sensor, so my CTS resistor mod DOES work on a US spec OBD I '91-'95 4.0 with the same side effects that I already mentioned.
The '96+ OBD II system isn't as forgiving when it comes to electronic trickery so it's possible that my CTS mod might cause problems there. My MAP adjuster mod also works fine on OBD I but not on OBD II.

[8Mud]

Some of the temp. switches sit pretty flush with the length of the stock thread, some are longer and hang into the coolant flow a touch. If you have the threads soldered on the radiator and don´t plan on opening a hole into the coolant flow, make sure the temp. switch is short enough or the threads are long enough.