How do I check to see if the fan clutch is bad?

Trying to diagnos my slight issue of overheating. I have had the system flushed and burped, and pressure tested, and it is fine. However, I still get a faint whif of coolant when I walk by the Jeep and cant figure out where it is coming from.

The XJ runs over 210, by just about a needles thickness or more when driving in town. It runs hot on the highway too. Yesterday it jumped to almost the redline when I exited the highway and my spped was around 25mph.

So here are my questions:

How do I check to see if the fan clutch is bad or not?

How do I check the t-stat and various other things.

I guess what I am looking for is the trouble-shooting process that will go from the simplest solution, to the most complicated, eliminating factors on the way.

Thanks for the help.

Fergie

I'm sure mine is bad after today. I drove around town and let it get nice and warm 210-212, then I popped the hood while it was still idling, then I reached in and turned the key off while I watched the fan. It free-spun 5-10 full revolutions. Try that out, or once it's nice and warm shut it off and spin it with your hand, I've heard you shouldn't be able to spin it more than 2 revolutions.

fan clutch stuff-
you can get two kinds- thermal and spring. Almost everyone has thermal.
The hotter it gets, the tighter it gets. On a hot engine it should be hard to spin, a cold engine easier. If the fluid inside the clutch is shot, it wont tighten up and it`ll almost freewheel-
Check when hot- grab the fan on opposite sides and try to rock it- if it rocks and feels loose, replace- it should rock a hair, but not so much you can hear it. Spring loaded clutchs eat up horsepower and sound louder the faster you go---

Simple suggestions. Replace the thermostat- I run a 160 (and havent had problems, ever, with open loop) And check to see if the aux fan is working- at 210 it should be on without the ac running. If it isnt, consider running a switch to the relay so you can run it when you need it. The temp sender for the fan should be on the radiator/drivers side- not the one in the block(89 series)-they do go bad, they sometimes fix themselves...they have gremlins inside them...take your pick.

Both my old XJ, and my DD MJ run at high 170+ untill I hit a hill, then jump to just under 210- either going back down the hill, or flipping the aux fan on instantly cools it.

The lead tech and service writer at my dealership both say there is no reliable way to test a fan clutch. My brother's best friend is a retired Jeep shop foreman and service manager. He says the same. Basically, if it's five years old or more it's suspect. The symptom of a failing fan clutch (sounds like the title of an Agatha Christie mystery novel) is heating up quickly when the vehile is standing, then cooling down quickly as soon as the vehicle gets moving. If the overheating is at highway speed, the fan clutch isn't the problem ... or at least not the only problem.

Thermostats ... some people say to change it every two years. Certainly, if the engine has overheated the t-stat should be replaced.

Another thing that can cause overheating at highway speeds is aftermarket lower radiator hoses with no internal spring. When the hose gets warm and soft, the suction causes the hose to collapse and that shuts off all circulation through the radiator.

There are instructions in the FSM for testing the fan clutch. You have to hook up a timing light, cover the grill in plastic (to restrict the airflow), drill a hole in the fan shroud, and insert a thermometer. At 190F, the clutch should kick in and start running a lot faster. I have done this and you can see(with the timing light) it going faster, you can hear it going faster, and you can feel more air coming out.

The disadvantage of this test: Even though your fan might be going faster, what this test does NOT do is measure the volume of air being pulled through the radiator. I ended up replacing mine even though it passed the above test.

Here’s another thing that I did which seemed to lower the cooling by about 5 degrees:
I got ¼” thick foam insulation tape and covered all the openings around and between the two fan shrouds. That way, more air was being pulled through the radiator, rather than coming from the sides of the fan shrouds.

Well, I know that the other day, when I turned the vehicle on, the main fan was on right away. Is this suppossed to happen? Before I turned the vehicle on, I checked the fan an it wouldnt turn more than half a revolution before it stopped, probably more like a quarter revolution.

The only time I can really get the aux fan to come on is to hit the AC and force it to come on.

For my edification, what is "overheating" defined as, temperature wise? In the redline or going above 210?

Thanks for the help and the info.

Fergie

what's a normal price for a new fan clutch?

Fergie said:

For my edification, what is "overheating" defined as, temperature wise? In the redline or going above 210?

Click to expand...

"Overheating" is getting into the red zone. Running above 210 but below the red would be "running warm." 210 is normal.

BrettM said:

what's a normal price for a new fan clutch?

Click to expand...

I replaced mine about 6 months ago and IIRC it was about $40-$50 at Autozone.

Okay, the lower hose isnt collapsing when coolant is going through.

The jeep runs "warm" during town driving, one to two needle thickness' above 210.

My main question is, should the main fan be on all the time? Mine comes on when I start the Jeep. I cant sping the fan much more than a few blades passing by, and it is even tougher when the Jeep has been running.

So, does it sound like I have an overheating problem, or am I paranoid?

Fergie

PS- My gauges have been switched from idiot lights. When I had lights only, my overheat light never came on.

The primary fan always spins. There is no "on" with respect to the mechanical fan. The fan clutch only determines how hard the engine makes it work -- it's always spinning, but loosely unless it's needed.