Electric fan has new sensor but does not work
12-12-2010, 12:07 AM
#1
Newbie
Thread Starter
Join Date: Nov 2010
Posts: 16
Likes: 0
Received 0 Likes
on
0 Posts
Model: Cherokee
Electric fan has new sensor but does not work
Hi folks.
i did a complete rebuild of my cooling system on my 91 XJ with the 4.0. including both cooling sensors. the one wire sensor located in the back of the head for the gauge works fine.
The one in the thermostat housing on the other hand only kicks the fan on when the AC compressor is turned on, but not when the vehicle is at operating temperature (210).
i used a little Teflon tape on the threads and was careful not getting the tape anywhere it didn't belong.
the fan will come on when i disconnect the connector from the sensor, and then go back off when I hook it back up.
i did a complete rebuild of my cooling system on my 91 XJ with the 4.0. including both cooling sensors. the one wire sensor located in the back of the head for the gauge works fine.
The one in the thermostat housing on the other hand only kicks the fan on when the AC compressor is turned on, but not when the vehicle is at operating temperature (210).
i used a little Teflon tape on the threads and was careful not getting the tape anywhere it didn't belong.
the fan will come on when i disconnect the connector from the sensor, and then go back off when I hook it back up.
12-12-2010, 12:16 AM
#2
Seasoned Member
Join Date: Jan 2010
Location: Midlothian, VA
Posts: 336
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1996
Model: Cherokee
Engine: 4.0
Sounds like its working fine to me the fan should only come on with a/c on or if its over heating. It comes on when the senors disconnected because the computor cant tell if its getting hot so turns it on all the time to prevent over heating
12-12-2010, 12:37 AM
#3
Newbie
Thread Starter
Join Date: Nov 2010
Posts: 16
Likes: 0
Received 0 Likes
on
0 Posts
Model: Cherokee
I have a 180 thermostat and wouldnt expect it to be past 200.
when the vehicle is in motion it stays at a steady 205
12-12-2010, 01:23 AM
#4
Seasoned Member
Join Date: Sep 2009
Location: Everett, WA
Posts: 373
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1990
Model: Cherokee
Engine: 4.0l
Welcome to the Cherokee Forum! 
You might have a bad "new" sensor, its happened to me before. I've heard mixed numbers on when they're suppose to click on, but I've heard a lot of guys say its too hot anyway, so they just run a bypass switch to turn it on when they want. I'm running a bypass switch and almost never need it.
Id be more concered about your running temp, especially for this being the winter and the 20 degree difference between idle and running. One possibility is a stuck thermostat. If you have everything new(rad., heater core, hoses etc.), and I where you, I'd pull your thermostat and make sure it not crooked, if it is, reinstall it right and see what happens. If it looks fine, take it out and put it in a pot of water and start heating it with a thermometer(candy or meat) in it to tell you the temp. You should be able to watch the thermostat open around 175 to 185 degrees. Also a bad radiator cap can create an overheat problem, they're cheap and should be replace regularly.
Did you flush the block before installing your new cooling system? I've heard of guys installing a new radiator and plugging it up the next day because the block was full of crap.
You might have a bad "new" sensor, its happened to me before. I've heard mixed numbers on when they're suppose to click on, but I've heard a lot of guys say its too hot anyway, so they just run a bypass switch to turn it on when they want. I'm running a bypass switch and almost never need it.
Id be more concered about your running temp, especially for this being the winter and the 20 degree difference between idle and running. One possibility is a stuck thermostat. If you have everything new(rad., heater core, hoses etc.), and I where you, I'd pull your thermostat and make sure it not crooked, if it is, reinstall it right and see what happens. If it looks fine, take it out and put it in a pot of water and start heating it with a thermometer(candy or meat) in it to tell you the temp. You should be able to watch the thermostat open around 175 to 185 degrees. Also a bad radiator cap can create an overheat problem, they're cheap and should be replace regularly.
Did you flush the block before installing your new cooling system? I've heard of guys installing a new radiator and plugging it up the next day because the block was full of crap.
12-12-2010, 07:52 AM
#6
CF Veteran
Join Date: Mar 2010
Location: Broward County Fl.
Posts: 47,923
Likes: 0
Received 22 Likes
on
22 Posts
Year: 1989 xj sport 2dr
Model: Cherokee
Engine: 12 hole bosch Injectors
Hi folks.
i did a complete rebuild of my cooling system on my 91 XJ with the 4.0. including both cooling sensors. the one wire sensor located in the back of the head for the gauge works fine.
The one in the thermostat housing on the other hand only kicks the fan on when the AC compressor is turned on, but not when the vehicle is at operating temperature (210).
i used a little Teflon tape on the threads and was careful not getting the tape anywhere it didn't belong.
the fan will come on when i disconnect the connector from the sensor, and then go back off when I hook it back up.
i did a complete rebuild of my cooling system on my 91 XJ with the 4.0. including both cooling sensors. the one wire sensor located in the back of the head for the gauge works fine.
The one in the thermostat housing on the other hand only kicks the fan on when the AC compressor is turned on, but not when the vehicle is at operating temperature (210).
i used a little Teflon tape on the threads and was careful not getting the tape anywhere it didn't belong.
the fan will come on when i disconnect the connector from the sensor, and then go back off when I hook it back up.
12-12-2010, 07:55 AM
#7
The PCM turns the aux. fan on at 213 deg F.
A 80 deg. t-stat won't make the rig run cooler, it simply opens 15 deg earlier than a stock t-stat.
There is only 1 sensor, it's located in the water neck adjacent to the t-stat. The coolant temp sending unit is located on the rear corner of the cylinder head (driverside).
The temperature indicated may not be correct, wgich is common with a bad sending unit. Replace the sending unit, it's gonna set ya back about $25.
A 80 deg. t-stat won't make the rig run cooler, it simply opens 15 deg earlier than a stock t-stat.
There is only 1 sensor, it's located in the water neck adjacent to the t-stat. The coolant temp sending unit is located on the rear corner of the cylinder head (driverside).
The temperature indicated may not be correct, wgich is common with a bad sending unit. Replace the sending unit, it's gonna set ya back about $25.
Trending Topics
12-12-2010, 08:34 AM
#9
Newbie
Thread Starter
Join Date: Nov 2010
Posts: 16
Likes: 0
Received 0 Likes
on
0 Posts
Model: Cherokee
Fan clutch is new as well.
I already bought it, so I should be able to exchange it.
The PCM turns the aux. fan on at 213 deg F.
213? seems a bit high. guess its more for emission purposes. They want to burn as much gas as hot as possible till they want the engine cooled.
A 80 deg. t-stat won't make the rig run cooler, it simply opens 15 deg earlier than a stock t-stat.
There is only 1 sensor, it's located in the water neck adjacent to the t-stat. The coolant temp sending unit is located on the rear corner of the cylinder head (driverside).
I replaced that sensor as well. I thought that one was for the guage since it only has one wire, and the pcm controlled for the fan was the two wire located in the thermastat housing.
The temperature indicated may not be correct, wgich is common with a bad sending unit. Replace the sending unit, it's gonna set ya back about $25.
213? seems a bit high. guess its more for emission purposes. They want to burn as much gas as hot as possible till they want the engine cooled.
A 80 deg. t-stat won't make the rig run cooler, it simply opens 15 deg earlier than a stock t-stat.
There is only 1 sensor, it's located in the water neck adjacent to the t-stat. The coolant temp sending unit is located on the rear corner of the cylinder head (driverside).
I replaced that sensor as well. I thought that one was for the guage since it only has one wire, and the pcm controlled for the fan was the two wire located in the thermastat housing.
The temperature indicated may not be correct, wgich is common with a bad sending unit. Replace the sending unit, it's gonna set ya back about $25.
12-12-2010, 08:36 AM
#10
Newbie
Thread Starter
Join Date: Nov 2010
Posts: 16
Likes: 0
Received 0 Likes
on
0 Posts
Model: Cherokee
Im going to remove the teflon tape and see if that makes it kick on.
Ill post the results.
Also, I did flush the block as well. I didnt want to gum up a brand new radiator and head.
Ill post the results.
Also, I did flush the block as well. I didnt want to gum up a brand new radiator and head.
Thread
Thread Starter
Forum
Replies
Last Post
Aryl
Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go here
10
04-10-2019 09:07 AM
Chick-N-Picker
Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go here
21
08-27-2015 12:27 PM
moparchero
Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go here
0
08-26-2015 12:58 PM
Rad Vlad
Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go here
7
08-20-2015 07:44 PM
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)