ftpiercecracker1 Posted January 14, 2012 Share Posted January 14, 2012 1990, eliminator, 5spd, 4.0 Fan fails to kick on as engine temp increases, resulting in continuous overheating. motor is good. 100% certain computer temp switch, put in tonight. bad relay maybe? There is one on the driver side fender well that when you jump the wires kicks the fan on, but I've been told that one is for the a/c and defrost and that there is another one somewhere else dedicated to the engine temp and whether or not the fan kicks on. any help would be great, i've also been told that there could be a chance that that particular pin in the ECU could be burned up, the one that controls the fan. What would be the odds of that? thanks for the help Link to comment Share on other sites More sharing options...
Jeep Driver Posted January 14, 2012 Share Posted January 14, 2012 If it were me............ I'd just run a new fan circuit. I believe you said you installed a new temp switch? 14 gauge wire, few connectors, tape, solder, and a new relay.......cost like $12 to $15. Link to comment Share on other sites More sharing options...
Eagle Posted January 14, 2012 Share Posted January 14, 2012 Fan fails to kick on as engine temp increases, resulting in continuous overheating.motor is good. 100% certain computer temp switch, put in tonight. bad relay maybe? There is one on the driver side fender well that when you jump the wires kicks the fan on, but I've been told that one is for the a/c and defrost and that there is another one somewhere else dedicated to the engine temp and whether or not the fan kicks on. You were told wrong. That IS the relay for the aux fan. The ECU in the Renix-era MJs does not have any control over the aux fan -- that came in with the Chrysler system in 1991. However, the relay may not be bad. Which wires are you jumping to actuate it? For pure temperature, the relay is triggered by a sensor in the driver's side radiator tank. If that sensor is bad or there's a break in the wires between the sensor and the relay ... the relay won't get triggered. As a work-around while you diagnose the problem, you can wire a toggle switch to the relay control terminals and control the fan manually. But ... where are you located? It's January -- winter. Not all MJs even had an auxiliary fan. If you are experiencing overheating in January, your radiator is probably due to be replaced, or else the fan clutch on the mechanical fan is bad. The primary fan should be all you need this time of year. Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted January 14, 2012 Author Share Posted January 14, 2012 The sensor on mine is located on the driver side of the engine block, just above the engine mount, and its brand new, replaced it last night. I think the problem lies somewhere between the relay and sensor (ground?), i will have to trace it to find out. I know the relay is good, because the fan does kick on each time the a/c is turned on. Would you happen to know what temp it requires for the aux fan to kick on? I drove the truck today on some back roads and mild trails and it never got above 212*, but the fan never kicked on. By the way, the rad is one year old, same with the pump, and the t-stat is brand new, replaced it last night as well. Fan clutch is good as well, pulls hard. Link to comment Share on other sites More sharing options...
JeffN Posted January 14, 2012 Share Posted January 14, 2012 the fan won't kick on till it is around 230 degrees i think, or if the A/C is on or defroster (which turns the compressor on). I believe only trucks with A/C came with an aux fan Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted January 14, 2012 Author Share Posted January 14, 2012 dadgum you guys are FAst. :cheers: thanks for the info is there a way to adjust that? the temp i mean. Link to comment Share on other sites More sharing options...
Jeep Driver Posted January 14, 2012 Share Posted January 14, 2012 dadgum you guys are FAst. :cheers: thanks for the info is there a way to adjust that? the temp i mean. Change the switch. Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted January 14, 2012 Author Share Posted January 14, 2012 tooo what? what would i ask for at an auto parts store? I would like the fan to kick on at about 215* instead of 230. I just don't like it getting that hot before there is some relief. These trucks are bad about warped heads because of overheating. Link to comment Share on other sites More sharing options...
mythreesons Posted January 15, 2012 Share Posted January 15, 2012 You were told wrong. That IS the relay for the aux fan. The ECU in the Renix-era MJs does not have any control over the aux fan -- that came in with the Chrysler system in 1991. The sensor on mine is located on the driver side of the engine block, just above the engine mount, and its brand new, replaced it last night. I thought that there were three temp sensors??????? Driver side- top for idiot light/temp guage, driver side below exhaust for ECU (open/closed loop operation) and the driver side radiator for aux. fan control. Maybe your missing a sensor in the radiator? Link to comment Share on other sites More sharing options...
Jeep Driver Posted January 15, 2012 Share Posted January 15, 2012 tooo what? what would i ask for at an auto parts store? I would like the fan to kick on at about 215* instead of 230. I just don't like it getting that hot before there is some relief. These trucks are bad about warped heads because of overheating. https://www.advancedsportvehicles.com/s ... uct_id=248 When I get a 4.0 keeper XJ I will install duel electric fans. The primary will run off the switch listed above and will be installed in the thermostat housing. The secondary will run off the switch installed in the radiator and will be rated to cycle around 210. Image Not Found Image Not Found I have not run a clutch fan since '04, don't like them, have no tolerance for them, will not have them. Don't want one in my way. Further I want to run cool, I understand that I need to maintain a correct running temp to sensors and ECU to run fuel and timing correctly.....200-210 is the range I want to run in, no hotter and no cooler. I'll build the system that works for me, not what a manual says, not what a particular OEM switch dictates......but what I want. Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted January 15, 2012 Author Share Posted January 15, 2012 still, where can i go to get a temp sensor calibrated for 215* instead of 230?? Link to comment Share on other sites More sharing options...
Jeep Driver Posted January 15, 2012 Share Posted January 15, 2012 still, where can i go to get a temp sensor calibrated for 215* instead of 230?? They are available. One rated as the one I posted above at 195 will actually close and turn the fan on around 200-205, none are that accurate. As I stated above, I will get one rated at 185 that will actually cycle around 195 to run my primary and I will get one rated at 195/200 to cycle around 205-210 to run my secondary. Realize that your fan has to play catch-up, by the time you are cycling at 205 your are approaching 210 about the time the cooled coolant is ready to pass through the thermostat. SPAL makes a fully adjustable unit, controls two fans but costs around $150 IIRC but is a true digital controller......very nice but pricey. Link to comment Share on other sites More sharing options...
Jeep Driver Posted January 15, 2012 Share Posted January 15, 2012 https://www.advancedsportvehicles.com/s ... uct_id=248 Link to comment Share on other sites More sharing options...
Jeep Driver Posted January 15, 2012 Share Posted January 15, 2012 Sorry.........you were asking particularly which one for the 215. BWD TFS8, 3/8NPT and a closed temp of 204 degrees, fits the mid 80s Corvette and Camaro V8s. Actually closes around 210 and about as close and you will get. Others are available but in metric thread sizes. Most have been discontinued I believe because most of the modern engines are running higher temps. Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted January 15, 2012 Author Share Posted January 15, 2012 ok, so a little update. Its about 35* outside, I took the truck for a short spin and the temp fluctuated between 213 and 185. In low range creeping up a hill side the temp wouldnt come down from 215* and the whole time the fan never kicked on. So 1. What exactly is my running temp supposed to be? 2. Why is my fan still not kicking on? I know for a fact the relay is good and the sensor is new. 90, eliminator, 5spd, 4x4, 4.0, fan temp sensor is on the driver side engine block, inbetween the engine mount and exhaust. Relay is on the driver side inner fender well. Link to comment Share on other sites More sharing options...
MJCARENA Posted January 15, 2012 Share Posted January 15, 2012 The sensor in the block on the drivers side by the mount is for the ECU not the fan. The fan sensor is on the drivers side on the radiator by the outlet hose. Like others have mentioned the fan will not kick in till around 230 degrees or if you turn on the AC if you have it. From what I understand 210-215 is normal temps for the Renix 4.0, that is where both my XJ and MJ run at. Link to comment Share on other sites More sharing options...
cruiser54 Posted January 15, 2012 Share Posted January 15, 2012 Coolant Temp Sensor is on the side of the block. Temp SENDER for the gauge is at the back of the head. Electric fan sensor is in the driver's side of the radiator on a 1990. Have you changed to an open cooling system or still have the original? Link to comment Share on other sites More sharing options...
Eagle Posted January 16, 2012 Share Posted January 16, 2012 The sensor on mine is located on the driver side of the engine block, just above the engine mount, and its brand new, replaced it last night. Nope. THAT sensor sends input to the ECU, but it controls whether the ECU is in open-loop or closed-loop mode. That sensor has nothing to do with the aux fan. Link to comment Share on other sites More sharing options...
Eagle Posted January 16, 2012 Share Posted January 16, 2012 Would you happen to know what temp it requires for the aux fan to kick on?[/color] I drove the truck today on some back roads and mild trails and it never got above 212*, but the fan never kicked on. Never gets above 212? That's below normal for an MJ. What did you mean when your original post said Fan fails to kick on as engine temp increases, resulting in continuous overheating. Overheating is when the needle on the gauge is constantly in the red zone, which is around 240 degrees and up. Are you overheating, or not? Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted January 16, 2012 Author Share Posted January 16, 2012 everything is stock, but not original, still a closed system I know this may come off as a little anal but 230 is just to long to wait for the fan to come on to me. Is there a sensor that would kick the fan on sooner? say 215? I know about the earlier posts, and his suggestion, but is that my best option? Link to comment Share on other sites More sharing options...
shelbyluvv Posted January 16, 2012 Share Posted January 16, 2012 You do understand that this is a fuel injected vehicle and not a carbed one? FI engines like more heat in them to run at optimal temperature. If you start over cooling the engine you can actually seriously hurt the engine and fuel economy. It is running normal. Leave it alone before you do have a problem. Link to comment Share on other sites More sharing options...
Jeep Driver Posted January 16, 2012 Share Posted January 16, 2012 everything is stock, but not original, still a closed systemI know this may come off as a little anal but 230 is just to long to wait for the fan to come on to me. Is there a sensor that would kick the fan on sooner? say 215? I know about the earlier posts, and his suggestion, but is that my best option? Yeah I was only suggesting you can find other switches and create your own system that works for you, and cheaply too. It's not at all complicated. BTW.......just my experience with 4.0s...... When they get hot they get hot fast, 210 to 250/260....real fast. Nothing worse than a 6 mile incline at 7-8% grade and hitting red 3/4 of the way up. Link to comment Share on other sites More sharing options...
Jeep Driver Posted January 16, 2012 Share Posted January 16, 2012 You do understand that this is a fuel injected vehicle and not a carbed one? FI engines like more heat in them to run at optimal temperature. If you start over cooling the engine you can actually seriously hurt the engine and fuel economy. It is running normal. Leave it alone before you do have a problem. I look through about 300 to 400 CL ads per day.....maybe more. I would say that 1 out of every 9 needs a head gasket, has a cracked head, overheats, has a seized engine, or has had the head gasket recently replaced due to overheating. And I wonder how many trans have gone out due to heat? I will stay on the cool side of hot. 210 works for me. Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted January 16, 2012 Author Share Posted January 16, 2012 Thank GOD for the comanche club! What I would do without you guys is a mystery. I found the sensor on the rad, unpluged it and tested, what do you know fan kicked right on. Now i just need to know where to get a lower rated temp sensor. And just to let the guy know who posted his suggestion of a different senor, it won't work, mine seems to be much larger. thanks again Link to comment Share on other sites More sharing options...
Jeep Driver Posted January 16, 2012 Share Posted January 16, 2012 Thank GOD for the comanche club!What I would do without you guys is a mystery. I found the sensor on the rad, unpluged it and tested, what do you know fan kicked right on. Now i just need to know where to get a lower rated temp sensor. And just to let the guy know who posted his suggestion of a different senor, it won't work, mine seems to be much larger. thanks again I know it is. You may or may not find a desirable temp in that size.......you may have to find an adapter. Imagination. You may have to relocate it to suit your needs. Enginuity. Link to comment Share on other sites More sharing options...
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