Auxiliary Fan

Here’s my problem. My aux fan is not coming on when the engine is hot. It runs in all three A/C positions. As long as I’m moving its fine but stop in traffic and it starts makin me real nervous. The other day it actually overheated after a backed up freeway incident. I did a search on this, but I still have some questions remaining.

Is that the temp. sensor that operates the fan above the big radiator hose on the driver side, and are they prone to failure?

If I want to ad a dash switch as a manual “on” override where is the best spot to hook it in? Is there a relay? Anyone know wire colors or any specifics like that? Thanks

Bronco said:

Thanks for the info. I’m thinking at this point id rather hook into the relay (if I could find it). It seems like it could be done with only one wire. Run through the firewall.

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It's your Jeep, but the way I am talking about is easier and won't change the stock setup.

You said the electric van not comign on when you think it should. being an owner of a Renix XJ here what I have learned.

Electric fan comes on at either:
1) AC clutch is engaged
2) Tempearature in the "cold" tank of the radiator has reached 190F. There is a switch which turns ON and OFF the electric fan.

Your profile says this is an 87 XJ, have you done much cooling system maintenance?

* How old is your radiator, you still could have the stock radiator and if so it is due for replacement.
* How old is the fan clutch for the mechanical fan, if it over 5 years old replace it. There is no good way to test one to see if it working.
* Do you have the temp sensor in the cold tank of the radiator connected to the chassis harness? The fan can not turn on if it does not ther the "signal".

If you have been over heating or getting the XJ hot I'd replace these items.
1) Thermostat - get at the dealer, comes with the gasket.
2) Pressure tank - on the firewall, get it for $20 from quadratec.com and it comes with a new "radiator" cap.
3) Mechanical fan clutch - once you have it out of the vehicle take it to the parts store so you get the same height unit.

If that does not do it then I'd consider replacing the radiator. The radiator may be full of crud and can not get out the heat.

You may have water pump with an impeller that rotating on the shaft, not likely but could explain stuff. If you have the radiator out this would be a perfect time to change the water pump, you will never have that much room again. If you change water pump then install a new belt and use the Kriket II from NAPA to tension the belt. I also repalced the idle pulley and the bearing assy for the mechanical fan. You have to buy the AC compressor bracker at the dealer to get the new fan bearing.

I think you are due for cooling system maintenance. It sounds like a bad mechanical fan and a partially stopped up radiator. I changed my radiator in Feb this year, not a bad job.

Martin

That is all fine advice; however tell me if I’m wrong here the aux fan should be on if the engine is overheating? Whatever ells may be wrong, the fan should be coming on right? Up till last week the only time my jeep has overheated on me was when the water pump went out. Now in conjunction with the stopped on the freeway overheating episode I also found the water level was low and that I had very slow leak at the radiator. I guess what I'm saying is I’d like to address the most obvious problems first. The leak is kinda straightforward; what are the possible reasons for the fan not working? I did read somewhere that if the radiator was clogged up the time for the water to cross the grid was increased and therefore colder water was reaching the sensor and it wouldn’t trip the fan, but that sounds like a long shot, and like you say replacing the radiator is what you do after you do everything ells first and it doesn’t work. Thanks for your help and ideas.

Bronco said:

Here’s my problem. My aux fan is not coming on when the engine is hot. It runs in all three A/C positions. As long as I’m moving its fine but stop in traffic and it starts makin me real nervous. The other day it actually overheated after a backed up freeway incident. I did a search on this, but I still have some questions remaining.

Is that the temp. sensor that operates the fan above the big radiator hose on the driver side, and are they prone to failure?

If I want to ad a dash switch as a manual “on” override where is the best spot to hook it in? Is there a relay? Anyone know wire colors or any specifics like that? Thanks

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Use a relay and toggle. White wire is (+), black is (-) on the fan. If you splice into the existing wires to the relay, you will be able to manually turn on your fan via toggle or let the ECU turn it on w/AC or engine over 218*. You can place the relay under the front of the hood under the front end lip. If you're still overheating with the aux fan on, you may need to replace your clutch on your belt fan.

Planetcat, the 87-90 XJs engine computer is totally different and does not operate like your later model XJ. It is a common mistake. The Renix ECU does not turn on the electric fan due to temperature of the coolant.

Bronco, examine your radiator and find the temp sensor located in the "cold" tank. Then follow the wire to the chassis connector - should be around the air box snout - and un plug. With the vehicle off put a jumper wire across the terminals of the chassis harness then start your XJ. If the fan runs then I'd say that switch in the cold tank may be bad. I got a new one for $19 at the parts store when I changed my radiator. You will have to drain coolant to change the sensor.

If you jumper it and the fan does NOT run then you may have more wiring problems. There is a diode assy used to provide power to the relay. I find it hard that it has failed but always can happen.

If you find the jumpering does not make the fan run you may want to consider turning on the AC when the XJ starts running warm as a "limp home" fix until the problem is totally fixed.

If you have a radiator leak may I suggest you replace the radiator, do not try to fix it. I picked up a new Modine for $116 + tax at the Modine Dist in town. I had a slow leak out of the end tank crimp on my 4 year old GDI.

If you go with the radiator replacement then get the radiator hoses and heater hoses at the dealer. The radiator hoses are priced competitive with aftermaket and come with the antichafe on them already. The heater hoses from the dealer fit like a glove. I had used Goodyear brand and had to make some sections work and they only listed 4 of the 6 sections of hose. Dealer hoses are worth the money. Figure $40 for radiator hoses, $70 for heater hoses. I am suggesting you spend more money IF you change the radiator but replacing hoses is just smart money. You can also get the pressure bottle at the dealer but they run around $50. There is something to be said about getting the parts today vs waiting a week for the mail order pressure tank.

On your heater hoses, if they still have the aluminum bands at the heater control valve and the wye fitting then those are OEM hoses and should be replaced since they are the age of the vehicle. I try to change hoses every 4 years regardless of mileage.

I can go into more on radiator replacement if you like. I posted about it in the past 2-3 months.

Let me know how jumping the connetor test comes out.

I have one of those sensors laying around from my cooling swap you can flat out have for the shipping if that turns out bad, just pop me an address and I'll post it.

I don’t know why but haven’t been getting email notification on this thread. L I’ll try jumping it tomorrow. I looked at it yesterday and the wires from the temp switch went into a loom within two inches. How far do I have to go to find the connector? I’m not sure what you mean by “chassis harness” Do you mean just mean a harness plug where the sensor plugs in? All my hoses are fine and less then two years old. I have replaced the oem bottle with an aluminum one with a real cap (16psi). The radiator may be old and the coolant doesn’t look too good. O and I’m only assuming the clutch fan is up to snuff. The water pump is only three months old. I guess a new radiator and clutch wouldn’t hurt. Thanks for the help

Thanks Frank. I’ll let you know if I need to go that rough but for the $20 I’d likely just get a new one.

Bronco, The temp sensor has a pigtail which is around 6 inches long on it. You are seeing the "loom" on the pig tail. Just follow along and you will find the connector.

When I said chassis harness I mean the harness which is a perminate part of the vehicle chassis. This temp sensor connects to the chassis harness.

Welcome to owning an XJ, plenty of times you get to practice your mechanic skills!!!

martin said:

Welcome to owning an XJ, plenty of times you get to practice your mechanic skills!!!

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Ya last weekend I swapped my tranny for the second time in as many months.:repair: This weekend it looks like I need to swap this darn temp sensor. LOL

Thanks for your expert advise. I found the plug after a bit more lookin and got voltage across it, and then I jumped it and got a click from the relay (found it) and the fan roared to action. At this point I am assuming that the Temp switch is dead. If anyone sees a hole in my trouble shooting logic let me know. I picked up a new one at the dealer (it was almost $35 bucks:moon: ).

Bronco --

It would be a LOT easier to read your posts if you'd stop using bold face type. Bold is for emphasis, not for the entire message.

Pay attention to what Martin has written. The aux fan relay should be mounted to the driver's side inner fender, behind the air box. However, if you simply jumper the wires coming out of the radiator tank as Martin suggests, unless that test suggests that the relay is bad you don't even need to know where it is. If you want to add a toggle switch, just tap into both wires coming out of the radiator sensor, run both wires through the firewall to a switch, and you're done. You don't even need to know which wire is "hot" because all you're doing is closing the same circuit that the sensor closes.

Eagle, I generally appreciate your in depth understanding of Jeeps and the older XJs in particular, but I find no value in that last post whatsoever.
“aux fan relay should be mounted to the driver's side inner fender” I just said I found the Relay.
“If you want to add a toggle switch, just tap into both wires coming out of the radiator sensor, run both wires through the firewall to a switch, and you're done.”
At this point in the thread that is well-covered ground. Do you have some problem with me exploring the possibility of doing it another way?
Thank for the education on the use of bold type. Believe it or not that’s the useful part of your post.

Bronco, I got my temp sensor at the parts store, they have a web site http://www.oreillyauto.com you can also mail order it from www.rockauto.com . Both sell it for less than $20. I got a borg-warner one with a lifetime guarentee for that price.

Also Eagle was giving you some very good advice. That diode assy I talked about makes it not quite as simple you may think. I will tell you the last person you want mad at you on here is Eagle, had is the oracle of XJ information.

I’m not trying to make anyone mad. I’m honestly sorry to everyone involved.

I’m no EE but I know my way around the around a circuit and I’d like to have some dialog on that subject. At this point I’ve got my immediate problem locked down (thanks for all the help), and I’m not really convinced I even need to have an in cab switch but I do like to have control of that kind of thing. I think that tapping into the relay would have two advantages. One you would only need to run 1 wire through the firewall and 2 there would be less current in that wire. Seems like it’s worth talking about.

What you would be tying into on the relay would be the control, or trigger, side. The high current circuit would still be the one that powers the fan.

The sensor in the radiator tank already activates the control circuit in the relay, so by tapping the two wires coming out of the radiator to a toggle switch you're just echoing the temperature-activated switch with a manual switch in parallel. Yes, it's two wires through the firewall instead of one, but you don't need any new power source, and you don't need any additional fuse protection for your "new" control circuit. And it's already a low-current circuit.