Eagle Posted February 17, 2008 Share Posted February 17, 2008 If you used the one for a '91 and newer XJ/MJ, it's NOT a switch, and it will not turn your fan on. Actually it is a switch and will work without issues; several (including myself) have done it without issues. The key is to use the wires as I stated above. They can be found in a ribbed protector running down the left hand inner fender. Out of this ribbed wiring sleeve will be a connector with a yellow and black wire. I just stumbled onto this thread after being away from it for awhile. I don't have a '91 FSM but I do have a '94 FSM, and I believe the systems are basically the same. The engine coolant temperature "sensor" in the thermostat housing is NOT a switch, it is a variable resistor. It sends data to the PCM, which in turn sends a signal to the fan control relay. Feel free to check it for yourselves. Link to comment Share on other sites More sharing options...
Eagle Posted February 17, 2008 Share Posted February 17, 2008 I'm thinking the stat housing may be the wrong place to mount the temp switch. The stock temp control switch for the aux fan is on the engine block, left side, and it closes and applies a ground (not power) to the ECU when the coolant temp reaches the high limit. The ECU then sends a ground to the aux fan relay coil to turn on the fan. Maybe the stat housing doesn't get hot enough to close the temp switch? Just guessing here........ :eek: No it's not. That sensor does not control the aux fan. Link to comment Share on other sites More sharing options...
86FUBAR Posted February 17, 2008 Share Posted February 17, 2008 I used that same fan relay setup and didnt like it at all so i switched to the Flexalite V.S.C and have nothing but good to say about it, a few bucks more but worth it . thats JMO Link to comment Share on other sites More sharing options...
HOrnbrod Posted February 17, 2008 Share Posted February 17, 2008 If you used the one for a '91 and newer XJ/MJ, it's NOT a switch, and it will not turn your fan on. Actually it is a switch and will work without issues; several (including myself) have done it without issues. The key is to use the wires as I stated above. They can be found in a ribbed protector running down the left hand inner fender. Out of this ribbed wiring sleeve will be a connector with a yellow and black wire. I just stumbled onto this thread after being away from it for awhile. I don't have a '91 FSM but I do have a '94 FSM, and I believe the systems are basically the same. The engine coolant temperature "sensor" in the thermostat housing is NOT a switch, it is a variable resistor. It sends data to the PCM, which in turn sends a signal to the fan control relay. Feel free to check it for yourselves. Correct, it's a varistor that takes a 5V signal from the ECU and sends back a voltage dependent on the sensed temp to trigger the aux fan relay. Link to comment Share on other sites More sharing options...
HOrnbrod Posted February 17, 2008 Share Posted February 17, 2008 I used that same fan relay setup and didnt like it at all so i switched to the Flexalite V.S.C and have nothing but good to say about it, a few bucks more but worth it . thats JMO Yes, but the Spal Automatic Programmable Fan Controller uses this voltage (must have a delta of ~.3V which it does) to control a fan. $48 on Ebay. This is what I'm using for my new electric fan that's going to replace the mechanical fan. Will let ya know how this works out Brett next week. http://www.spalusa.com/fans/automated/a ... anpwm.html Link to comment Share on other sites More sharing options...
HOrnbrod Posted February 17, 2008 Share Posted February 17, 2008 I'm thinking the stat housing may be the wrong place to mount the temp switch. The stock temp control switch for the aux fan is on the engine block, left side, and it closes and applies a ground (not power) to the ECU when the coolant temp reaches the high limit. The ECU then sends a ground to the aux fan relay coil to turn on the fan. Maybe the stat housing doesn't get hot enough to close the temp switch? Just guessing here........ :eek: No it's not. That sensor does not control the aux fan. Yeah, was dead wrong on that statement. :oops: I've since gotten smarter. Link to comment Share on other sites More sharing options...
Eagle Posted February 17, 2008 Share Posted February 17, 2008 We now have a fairly good display of why I think this whole "You have to convert to an open cooling system" thing is over-rated and totally misdirected. The open system has the exact same size radiator and cools exactly the same as the closed radiator. If the two systems are operating normally, the open system offers NO better cooling than the "closed" system. The weak point in the closed system isn't the radiator, it's the plastic surge tank on the firewall. When I replaced my original radiator in the '88 XJ back in 2000, I used a replacement "closed" radiator and I replaced the plastic tank with a Moroso racing surge tank. It's an aluminum cannister with a conventional fill neck that accepts a standard radiator cap. No more leaking plastic caps, no more overflowing coolant, no more problems. And I didn't have to go through any of the problems you guys are rediscovering, because my new radiator had a bung for the aux fan sensor. Link to comment Share on other sites More sharing options...
BLHTAZ Posted February 17, 2008 Author Share Posted February 17, 2008 We now have a fairly good display of why I think this whole "You have to convert to an open cooling system" thing is over-rated and totally misdirected. The open system has the exact same size radiator and cools exactly the same as the closed radiator. If the two systems are operating normally, the open system offers NO better cooling than the "closed" system. The weak point in the closed system isn't the radiator, it's the plastic surge tank on the firewall. When I replaced my original radiator in the '88 XJ back in 2000, I used a replacement "closed" radiator and I replaced the plastic tank with a Moroso racing surge tank. It's an aluminum cannister with a conventional fill neck that accepts a standard radiator cap. No more leaking plastic caps, no more overflowing coolant, no more problems. And I didn't have to go through any of the problems you guys are rediscovering, because my new radiator had a bung for the aux fan sensor. As they say...hind sight is 20/20 ;) I did research the swap, but obviously not enough. It seemed to me that it would be a fairly quick and easy thing to do and with a 3 row radiator I should not have to worry about cooling in Florida's hot temps. The swap itself was very easy, but I had no idea that the fan thing was going to take 6 weeks or more to figure out :headpop: . I am with Eagle on this one. I will NOT recommend that folks do this swap as it really is not worth the hassle...BUT, I am still happy to have it working properly now. Link to comment Share on other sites More sharing options...
Eagle Posted February 17, 2008 Share Posted February 17, 2008 My replacement "old style" radiator is a 3-row. With all metal tanks. Not only that, I now have increased coolant capacity. The original plastic bottle hold maybe a quart, but it's supposed to be only half-full when cold to allow for expansion. The Moroso tank I used holds 1-1/2 quarts, and with a conventional cap it gets filled right to the top. The filler neck has a bung for an overflow tube, which I connected to an aftermarket catch bottle, so my system now functions like an "open" system, holds more coolant than a conversion to a factory open radiator, and the aux fan operates exactly the same as it always did. Link to comment Share on other sites More sharing options...
jtdesigns Posted February 17, 2008 Share Posted February 17, 2008 Whats the system pressures of the closed system?? I ASSuMEd the open system would be better/easier for removing trapped air. I'm just brainstorming here, but wouldn't you be able to fill the closed bottle with the truck running to rid it of air?? I bet million of overheating problems in the closed systems are from air.. And another thing about using a fan is it cuts alot of drag off the engine. Hey Hornbord do you notice a change in throttle response? Link to comment Share on other sites More sharing options...
BLHTAZ Posted February 17, 2008 Author Share Posted February 17, 2008 Yes, the closed system overheating problems are very often due to air in the system, but it is not hard to bleed it out using the "temp sensor removal method". These engines use both a Mechanical fan and electric so unless you are replacing the mechanical fan with an electric to run two electric fans, there is no advantage in my particular situation. Link to comment Share on other sites More sharing options...
jtdesigns Posted February 17, 2008 Share Posted February 17, 2008 Yes, the closed system overheating problems are very often due to air in the system, but it is not hard to bleed it out using the "temp sensor removal method". These engines use both a Mechanical fan and electric so unless you are replacing the mechanical fan with an electric to run two electric fans, there is no advantage in my particular situation. Yeah I have an auxiliary fan, but jezz if its that much trouble then I think I'll just not put it on.. :oops: Link to comment Share on other sites More sharing options...
BLHTAZ Posted February 17, 2008 Author Share Posted February 17, 2008 If you have an electric that you are considering installing in place of your mechanical, it's not hard to do as long as you have the proper controller. My issue was going from a closed cooling system to an open by changing the radiator which forced me to find another way to operate the stock electric fan because the old temp switch was in the radiator, but the new radiator has no place for it. The controller that I am now using will actually control two fans, so if I want to change my mechanical to electric one day...it should be no problem. :D Link to comment Share on other sites More sharing options...
HOrnbrod Posted February 17, 2008 Share Posted February 17, 2008 Whats the system pressures of the closed system?? I ASSuMEd the open system would be better/easier for removing trapped air. I'm just brainstorming here, but wouldn't you be able to fill the closed bottle with the truck running to rid it of air?? I bet million of overheating problems in the closed systems are from air.. And another thing about using a fan is it cuts alot of drag off the engine. Hey Hornbord do you notice a change in throttle response? Haven't finished it yet, prolly next this week. Link to comment Share on other sites More sharing options...
HOrnbrod Posted February 21, 2008 Share Posted February 21, 2008 Not to steal the thread, but noticed you have what looks like a brand new condenser installed. That's not OEM is it? They were all painted black AFAIK. I'm going to convery to R134 over the winter 'cause it's getting too hard to find R12. This is one of the things I need. Where did you get it? Aftermarket? Thanks Link to comment Share on other sites More sharing options...
BLHTAZ Posted February 21, 2008 Author Share Posted February 21, 2008 Yes...I had to replace the condensor when my discharge line exploded as I could not get the line to come off of the old one. I got it through a local company here in Orlando called Cold Air Distributors. Link to comment Share on other sites More sharing options...
HOrnbrod Posted February 21, 2008 Share Posted February 21, 2008 Roger, thanks. :cheers: Link to comment Share on other sites More sharing options...
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