99 XJ, 4.0, AW4
Cold - I'd say I get a 1/4 rotation if I flick it hard as I can get my fingers on it.
Hot (after engine is up to full op temp) - I generally will only get it to turn maybe the distance of the width of 2 of the fan blades of rotation with the same effort of flicking by hand.

I ask because best of my knowledge I've got my cooling system in good working order. here's the list since my ownership last 4 years...
New t-stat, t-stat housing, new water pump, (those about 3 years ago)....within the last year a new higher flow "desert class" radiator, upper and lower hoses. cooling system flushed at time of that replacement.
In average temps the jeep will stay just that hair under the 210 mark on the gauge no matter what.... HOWEVER...If it's either above 90 F...or she sits running idle at full op temp in traffic..(time I'm referring to was about 70ish degrees out)..after sitting in that traffic barely moving and in gear the whole time, after about 10-15 mins, the temp did start to creep up a little passed the 210 mark on the gauge... Is there something that needs addressing here? or is this full on normal for our 20+ year old XJs?
Note... as soon as I start getting some actual air flowing through the radiator from forward movement above 20 mph, it goes right back down.
Thanks!

 

Sounds normal to me. Mine stays just before 210 during summer driving and in traffic, will go past and kick on the aux fan. That was before I flushed the coolant, I won't know if flushing improved anything until summer. Now that it is in the 30s and 40s it runs kinda cold at about 185-190.
Edit: Your temps sound normal to me, I have no idea about the clutch fan, someone else will have to chime in on that.

 

Count your blessings.
Or stop bragging

 

From what I've read and experienced, it sounds like you're good. Ours barely hits over 205, 210. As for the fan clutch, it sounds like it's doing what my fresh clutches do. This last summer, we were running a little hotter than I like( 210-220) when doing some hills that we had to do at a crawl, no real airflow. Took out the old one, compared it to the new, didn't seem to spin that much different. Doesn't seem that testing them that way is necessarily an accurate testimate to it's condition. Plus put a new one in my Bronco to replace one that defiantly leaked out. Again, they all felt very similar.

That being said, the replacement did run little cooler the next time we went out. It's cheap and easy enough that if there is doubt, might as well just do it.. I've read a little about using fan clutches off of different applications to increase the cooling. Someone else would have to chime in on that tho.

And like someone else said, a cooling system flush won't hurt a thing... But it sounds like you're ok.

 

As others have said, that's pretty normal behavior. When idling in traffic, the mechanical fan really doesn't spin very fast, so on hot days it's common for the temps to creep up above 210 and eventually the electric fan will come on at 218 and drop the temps. Pretty normal. What's not normal is if the temps keep going up even with the electric fan on. Flushing out the system will certainly help (use a hose), but I think a layer of rust builds up on the water jacket over the years and acts as an insulator. The only thing to do in that situation is use a rust dissolver like Thermocure. I'm about to do that in mine before I put in the new heater core.

As for the mechanical fan clutch, I'm not convinced the "spin test" is really all that conclusive. The best way to tell if it's working properly is to see what happens when the engine is hot and the clutch is engaged. The fan should spin up and make a roaring sound like in the video below. In the cold weather, it might not be possible to get the clutch to engage much, but it's pretty common in the summer.

 

Another thing to add, there are some proper ways to wire up the aux fans to a toggle for times you want/need more airflow. Depending on how 'stock' your system is, you might read up on wiring that up to keep the ECM function of automatically running the fan at 218, but being able to leave them run when you have a tendency to "overheat". We just hardwired it strait to a switch, turn her on when we start watching the temp gauge a little much.

 

I've never just sat there and seen how far it will climb. maybe that's been before the aux fan kicks in. Not sure.
Oh and not bragging lol.... if this is how it is supposed to work then great I will definitely count it as a blessing with this ole girl. I just like to be proactive when it comes to the old jeep than reactive whenever possible.

Does anyone know the approximate temp on the gauge where the aux fan should kick in due to temp alone? (meaning no other accessories that kick it on like the defrost, etc)
I can definitely tell the aux fan kicks right on when I turn that accessory on, but cant say that I'm hearing the aux fan when the temp needle just starts to creep to the other side of the 210 mark. Is that not high enough? or is there something wrong there?

Otherwise I guess the only other option I have to verify is next time the temp starts to creep up.. hopefully find somewhere I can pull over and visually inspect to see if it's kicked on or not.

Thanks for all the replies

 

Found this for a 2000 XJ:
RADIATOR FAN RELAY—PCM OUTPUT
DESCRIPTION
The electric radiator cooling fan relay is located in
the Power Distribution Center (PDC).
OPERATION
An electric radiator cooling fan is used with certain
models/engines. It is controlled by the Powertrain
Control Module (PCM) through the radiator fan
relay. Not Equipped With A/C: The relay is energized
when coolant temperature is above 103°C
(217°F). It will then de-energize when coolant temperature
drops to 98°C (208°F). Refer to Cooling Systems
for additional information. Equipped With
A/C: In addition to using coolant temperatures to
control cooling fan operation, a two-gang A/C high pressure
switch is also used to control cooling fan
operation. When equipped with this high-pressure
switch, the cooling fan will not operate each time
the A/C clutch is engaged. Refer to Heating and Air
Conditioning for additional information.

The thing about the fan clutch is that most of the time they gradually fail rather than all at once. IMHO they become inconsistant with their operation as they fail. So I suggest that if you don't know the history of the clutch and your having symptoms of it having issues replace it.

 

Good point on the clutch there EZ....and thanks for the info.... I'm sure that's probably the same specs for any 97+ so would be the same for my 99.
I had heard that too.... that's also the reason why I intentionally tested with the "spin" test after driving with it up to full op temp.... so I could see if it was spinning with little resistance or if it felt fairly solid. Because if it would have spun freely at full op temp, then I would know that the clutch was not working correctly and would need to be replaced. Mine was solid...so don't think that's an issue sitting at idle. (meaning it's spinning at the rpm it's designed to at idle and not slipping).

 

It's supposed to come on at 218*F. To test it, let it idle in gear (chock the wheels) after a drive, and you may want to block the radiator with a piece of cardboard or newspaper so the mechanical fan doesn't keep temps down. I recommend using an OBDII reader to keep an eye on the temps and verify that it's actually at 218 when the fan finally kicks on. When the fan starts, have a look at the gauge in the dash for reference.

 

Sadly when you use an obd2 reader on an engine with ONLY the temp sender in the thermostat for computer control and temp indication...the temps will function EXACTLY as programmed because when that single sensor gets to the resistance that the computer is looking for...the thing will happen. The trick is determining that the sensor resistance corresponds to the temperature of of the sensor programming. example if the sensor is perfect it should read around 675 at 212 deg the gauge should read 210 ish and at 218 the fan should turn on...If your sensor is off and doesn't read 675 until 220ish your gauge will read 210 when the temp is actually 220 ish.and the fan will not turn on until the actual water temp is up near 230 but the gauge will show 218. Without a 2nd sensor for comparison you are at the mercy of the accuracy of your single sensor. The actual range is more than these numbers but you get the idea

 

Thanks... will try that and see what the results are.

 

good to know as well... thanks! Will have to check this too just to make sure.

 

Yes, good point. I was thinking mostly in terms of not letting the engine overheat with the radiator blocked waiting for a possibly defective fan to come on. The tricky thing about the gauge in the dash is that it tends to stop around 220ish and only jump way up to 240 or so when you get that hot, so it's not linear at all, unlike the resistance reason coming from the sensor. Either way, it's still better than the gauges most newer cars have that are essentially just glorified idiot lights.

 

They say you can use an ir thermometer at the sender housing...i dont have one so i put the sender in a pot of boiling water and measure resistance...at least i know true 212 .i also own a decade box...a very accurate variable resistor....i then plugged in the resistance i measured from the sensor into the decade box and then connected the decade box to the temp sender wiring harness..needle reads straight up at 210. Close enough to 212 for me