Definitive way to check the fan clutch?

[87manche]

Finally after all this speculation about what constitutes a bad one. And also a way to trail fix it so you can drive until you get a replacement. I'm not sure if it's accurate, as I don't remember a bimetal spring, but that guy has been right before. Can someone verify?
http://autorepair.about.com/library/a/1h/bl262h.htm

 

[RichP]

The jeep fans are hydraulic, not bi-metal spring types. Anecdotal way, when the engine is cold like from overnite start the engine, the fan should roar for 20 or so seconds then quiet down. Thats the fluid redestributing.
FSM method, you need a long thermometer, drilla hole down between the leading edge of the fan and the rad core. Drop the thermostat down the hole so there is air flow going over it. Watch the temp goe up to operating temp. Block the front of the radiator with cardboard or something to stop air flow, watch the thermometer get hotter as engine temp climbs. Remove the air flow blockage and again look at the thermometer, you should see the temp drop several degrees. The FSM has the exact numbers but thats the FSM way of testing it, at least in my 98XJ and both wranglers..

 

[87manche]

that's what I thought. That's a shame. I was just hoping for an easy way to check it. I don't think that mine's bad, but I see enough overheating threads that this would have been nice.

 

[xjtrailrider]

This is odd because I just went out and checked, all 4 of my XJ's have the bi-metal spring, two of which have the end of the spring epoxied in place. I just bought a new clutch-fan for my 90' and it also had the bi-metal spring. Were thier just certain years that the clutch fans where installed with the bi-metal springs? My XJ's are 90', 95', 96', 00'. That pretty much covers the spectrum of Renix-OBDI-OBDII!

Just curious.

 

[scorpio_vette]

The jeep fans are hydraulic, not bi-metal spring types. Anecdotal way, when the engine is cold like from overnite start the engine, the fan should roar for 20 or so seconds then quiet down. Thats the fluid redestributing.
FSM method, you need a long thermometer, drilla hole down between the leading edge of the fan and the rad core. Drop the thermostat down the hole so there is air flow going over it. Watch the temp goe up to operating temp. Block the front of the radiator with cardboard or something to stop air flow, watch the thermometer get hotter as engine temp climbs. Remove the air flow blockage and again look at the thermometer, you should see the temp drop several degrees. The FSM has the exact numbers but thats the FSM way of testing it, at least in my 98XJ and both wranglers..

that method is for some of the newer vehicles, but i never did figure out exactly which ones. my 97TJ is like that.

but both my 95 and my 89 have the bi-metal spring. and my FSM for those years and older also describe the testing method where you disconnect the bi-metal spring and turn it 90degree counterclockwise.

i will tell you though that most mechanics at dealerships DO NOT perform that test. when a mechanic has doubts about the clutch fan they just replace them.

 

[87manche]

yeah, but for the home mechanic/my rig just overheated on the trail type of thing this may be a very good thing to know.

 

[scorpio_vette]

well there are only 2 fans and 1 test for each of them. so look at your fan, and if you have the bi-metal spring, do as described above. if you don't have the bi-metal spring, then you'll have to do the test for that one. (let me know if you need the writeup for that one and i'll pull it from the FSM)

oh and just on a sidenote......make sure you check your radiator. i had my jeep down for a couple months while building a new motor, and when i put everything back together i forgot to clean the fins in the radiator. they still had dirt in them from when i was stuck in the water. i couldn't figure out my overheating problem until somebody pointed that out. i overlooked the most simple thing of all. so i pressurewashed the radiator for about 4 minutes until i could see through all the fins again, and now it works great.

 

[Matthew Currie]

Random "stuck inside on a rainy day" thought...Assume that when the fan is disengaged, it only exerts a small amount of torque, but when it heats up and engages, the torque increases. In theory, if you could attach a string to the fan and some stationary object, said string strong enough to resist the cold torque, but not strong enough to resist the torque when it engages, you ought to be able to test it by holding the fan with the string. Block off the radiator to heat it up, and if after a little time it breaks the string, voila: clutch is good.
Ok, back to your regular programming.

 

[BrettM]

perhaps not difinitive... but a while back I was told to let it heat up to 210 (what it always runs at), turn the motor off, and immediately spin the fan by hand. I could get it to sping a couple full turns by hand so it definitely wasn't locking up.

 

[badron]

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i will tell you though that most mechanics at dealerships DO NOT perform that test. when a mechanic has doubts about the clutch fan they just replace them.
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The fan is general replaced as a last call. After everything else is checked. If ever thing else is OK then WHY check the fan just replace it.
The spring test cannot be done on all spring fans. Will damage some.
The air temp test is unreliable at best and can be very time consuming.
Side note: I have fix a good 15% of the REPORT fan problems by replacing or tightening the belt. Blowing out the rad or slowing down the idle on automatic cars.