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XJ Ask the Question Thread
Herp Derp Jerp
Join Date: Nov 2011
Location: Parham, ON
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12 Posts
Year: 1999
Model: Cherokee
Engine: 4.0L OBD-II
Herp Derp Jerp
Join Date: Nov 2011
Location: Parham, ON
Posts: 18,251
Likes: 0
Received 13 Likes
on
12 Posts
Year: 1999
Model: Cherokee
Engine: 4.0L OBD-II
Can someone explain the different functions of the clutch fan and the other electric fan under the hood?
I was told/under the impression that the clutch fan came on when the coil in the end of the clutch heated up from the radiator's heat and then began to turn and helped cool down the engine? radiator? but mine is always on when the car is running. I just replaced it last night and then spent some time watching my in dash temp gauge and the two fans. When the heater is turned on the second electric fan comes on for about 15-30 seconds and then stops; similarly when I turn the heater off. Dash temp gauge will sit around 210 and then run up to just under next has mark just short of first red section and then drop back to 210 or slightly below.
On the other dash gauge my psi will run up to about 55-60 based on hash marks and then drop to under 30 when at an idle or stop light.
Tstat was replaced yesterday as well with mopar oem replacement, about a month ago I did alternator and head gasket.
I do have a cracked exhaust manifold but that is getting fixed next week.
As you can tell by the question, I know little about the 91 XJ I own but am trying hard to muddle through my /heating up/overheating issues.
I was told/under the impression that the clutch fan came on when the coil in the end of the clutch heated up from the radiator's heat and then began to turn and helped cool down the engine? radiator? but mine is always on when the car is running. I just replaced it last night and then spent some time watching my in dash temp gauge and the two fans. When the heater is turned on the second electric fan comes on for about 15-30 seconds and then stops; similarly when I turn the heater off. Dash temp gauge will sit around 210 and then run up to just under next has mark just short of first red section and then drop back to 210 or slightly below.
On the other dash gauge my psi will run up to about 55-60 based on hash marks and then drop to under 30 when at an idle or stop light.
Tstat was replaced yesterday as well with mopar oem replacement, about a month ago I did alternator and head gasket.
I do have a cracked exhaust manifold but that is getting fixed next week.
As you can tell by the question, I know little about the 91 XJ I own but am trying hard to muddle through my /heating up/overheating issues.
Herp Derp Jerp
Join Date: Nov 2011
Location: Parham, ON
Posts: 18,251
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Year: 1999
Model: Cherokee
Engine: 4.0L OBD-II
CF Veteran
Join Date: Apr 2011
Location: Indianapolis
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Year: '99 and '91
Model: Cherokee
Senior Member
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Year: 1994 and 1996
Model: Cherokee
The clutch fan in these things is never totally disengaged. Somewhere out there I posted the actual numbers, but in a nutshell the clutch is supposed to lock up more just after the thermostat opens, and lock up fully before the electric fan is summoned (218-ish?). If your in-dash gauge is creepin toward red land I'd first make sure that it's accurate by checking with an IR thermometer, then probably just replace that clutch.
What about the function and operation of the other fan over to the drivers side of the radiator?
Sheepishly, what is an IR thermometer?
Junior Member
OK I'll try that, the clutch fan was replaced yesterday but it was a very new used on from an 87. The 87 had sat for about a year but the one on my 91 was toast.
What about the function and operation of the other fan over to the drivers side of the radiator?
Sheepishly, what is an IR thermometer?
What about the function and operation of the other fan over to the drivers side of the radiator?
Sheepishly, what is an IR thermometer?
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Year: 1994 and 1996
Model: Cherokee
OK, infrared, where am I testing to compare with my dash gauge?
What specific point am I pointing the infrared thermometer to compare the readings?
gee that google is amazing!
What specific point am I pointing the infrared thermometer to compare the readings?
gee that google is amazing!
Herp Derp Jerp
Join Date: Nov 2011
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Year: 1999
Model: Cherokee
Engine: 4.0L OBD-II
On dem Older Jeeps the in-dash gauge is a separate sensor, but the temp that really matters is the thermostat housing. Point it at that character and see if the thermostat is working properly. The sensor in the thermostat housing is the one the ECU uses to control the fan
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Year: 2000
Model: Cherokee
Engine: 4.0
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Year: 1994 and 1996
Model: Cherokee
Thanks again for the help!