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Mechanical fan switches off and on constantly?

D

DigJeepsBrah

NAXJA Forum User
Location
Ken Caryl, 5280
Jeep runs a tiny bit warm going up long mountain passes on 32" tires, not even to the first mark after the desired (210°) running temperature.

Seems like there's something wrong with my cooling fan.

It seems to engage and disengage very frequently idling. Obviously can't really tell when I'm moving when it's turning on, or if it is.

I have flushed my radiator twice(someone mixed dexcool and green before I owned it) in the last year and just installed a new thermostat with a flush a few days ago, the Jeep is staying a touch cooler, but still not staying on that 210° mark if I'm pushing the Jeep uphill in second and third gear for 20+ minutes.

I'm starting to think that fan or the clutch for it is malfunctioning?

Anyone have a similar issue that might be able to point me in the proper direction(hopefully at a pull yard - I just sunk entirely too much money into this thing in the last couple of months addressing issues for wheeling this summer)

Am I too worried about it? Is it okay for a 4.0 to get a little warm going uphill for extended periods of time? It will not completely overheat. It never has. The hottest it ever got was just barely to the next hash mark after 210.

I figured if I let this continue I'd risk damaging the head?

Thanks in advance.

Jeep also has a full exhaust system(from the header to the tailpipe) and a K&N cold air intake.
 
ehall said:
What year XJ and where are you?

Going uphill puts a pretty big load on the engine. If you're not even crossing the 210 mark then I wouldn't worry about it
Click to expand...

It's a '98 XJ and I'm in Colorado. The weather has been unseasonably warm the last week or so. 50-70°

However just last week I went wheeling in a blizzard, it was probably 12 degrees outside with a consistent breeze and it would still get just slightly above that 210 mark. - I hadn't installed the new tstat at that point.

It's getting almost to the mark after 210 when I'm pushing it, that's why I'm worried.

I've probably got some air in the system still and need to add a bit of coolant but I'm not expecting that to get me the results I'm after.
 
210 is normal. Next mark up is about 235 IIRC, which is hotter than normal but is alright when going uphill on a hot day with the A/C running.

The coolant temp gauge is driven by the sensor in the thermostat housing. You can verify the gauge by pointing an infrared temperature gun at the thermostat housing. Does the e-fan come on when temperature gets hot? That is triggered by the same coolant temp sensor that drives the gauge, and should come on around 225 IIRC. It also comes on when you activate A/C including the Defrost mode

The mechanical fan is activated by the coil spring on the front of the clutch, using ambient temperature. IIRC the clutch activates at about 170 degrees. Are you running the A/C? That would load the condenser and heat up the air. You can verify that it comes on the desired temperature with a thermometer and a heat gun (blow drier) and rolled up newspaper--with the engine running, stick the newspaper in the blades at low temp, see how much restriction, then heat the fan clutch and see if the restriction changes any.

Do you remember what radiator cap you bought? You need one that is clearly labeled as a relief cap so that it will blow off steam to the overflow bottle and draw coolant back in. With the right cap, the system will bleed itself pretty quickly.
 
I have a locking radiator cap(I'd have to run out and check which manufacturer). My A/C works, and I turn it on for maybe 15 minutes every couple of months just to "maintain" it. However I really never use it. I was thinking about deleting it actually.

So no, not running the A/C. Usually the opposite when the motor is working hard I'll crank the heat in hopes of keeping it cooler under the hood.

When I sit at lights though or go through a drive through, or nearly the entire time I'm wheeling it the fan comes on for a couple seconds, switches off for a couple of seconds, rinses and repeats... Constantly. Never ending. Shouldn't it stay on consistently?
 
You might have a clogged radiator. You mentioned DEXCOOL earlier, that stuff will turn into a wax/clay buildup if its left too long and/or blended with green coolant. My dad's Taurus had that junk, and I had to rebuild the whole cooling system, couldn't get rid of the wax.
 
Yeah, I've got that nasty copper colored gunk..

Trying hard to flush it, but I fear it's toast. Any recommendations for a nice, reliable, economical/middle of the road priced radiator?

You don't think there's anything wrong with the fan though? The switching off and on all the time?
 
If the gauge is true then the fans sound like they are coming on when they are supposed to. Then they go off again after cooling the engine down a bit. You can (should) test them per the instructions above to see if they are coming on at the right temperature.

It should not be getting hot in 12 degree weather.
 
Last edited:
12 degree weather in 4 low pushing through more than a foot of snow @ 5MPH though?

Just idling or driving down the road @ 12 degrees will not result in temps above 210. It'll idle all day @ 210, just not under a load. Which I guess would tell me the fans are working just fine and it is the radiator. Bummer.

I'll have to get a temp gauge and test the fans anyway out of curiosity now.

I'm reading I should be after a 2-3 row copper radiator? As apposed to an all aluminum replacement?
 
DigJeepsBrah said:
Seems like there's something wrong with my cooling fan.
It seems to engage and disengage very frequently idling. Obviously can't really tell when I'm moving when it's turning on, or if it is.
QUOTE]
Are you sure that it's isn't the A/C compressor you hear cycling?
The compressor runs when the dash HVAC control the "Defrost" position.
Many times I will hear an XJ's compressor cycling on and off every few seconds.
The fan's clutch has a viscous drive and does not turn on and off quickly, rather it slowly engages and disengages.

I agree that the checking the coolant temperature with an infrared gun is a good idea. XJ's coolant switches can be way out of calibration.
I tried sensors three before getting one that was accurate, got it at the Jeep dealer

I have tried several radiators in my XJ and several friends XJ.
The best found so far is Mopar's 'secret' HD radiator (52080104AC). I found it listed in the 2000 Mopar XJ's parts catalogue. It is a 1-1/2" thick, with a dual core. It has worked great in several XJs.
It isn't a cheap radiator. The best price today is at Rock Auto. It isn't listed under XJs, instead use the Part Number Search, at the top of the page and enter Mopar 52080104AC. Today it is listed at $219.47.
Also found it on Amazon for $225, with free shipping.
http://www.amazon.com/Mopar-5208-0104AC-Radiator/dp/B0049EQLA6

One other thing that isn't often talked about is dirty A/C condensers. The condenser sits in front of the radiator and, if it is plugged with dirt and deal bug, air flow can be seriously compromised.
My friends overheating XJ's condenser was so plugged that repeated cleanings could not clear it enough to eliminate the problem. A new condenser cure the problem
Click to expand...
 
Mechanical fan switches off and on constantly?
Click to expand...

Mechanical or did you mean electric fan?

If you meant the electric fan cycling on and off; When the HVAC switch is in defrost mode, the a/c will run. Cold temperatures will cause the A/C to cycle and so will the elec fan.
 
That's correct but his high temperature gauge indicates something else. I suspect the sensor is defective. If its off by +15 then it will show 225 when it actually means 210, will trigger the e-fan to come on, then turn it off again after temperature drops. Why he needs to test it first.
 
and yes, I did mean electric fan. The electric fan cycles off and on.

The system seems to be working well. I topped it off and burped the system today..

It very well could be the sensor. Are you talking about the sensor on the tstat housing?

Like I said, it doesn't heat up passed about 12:30 (if 210 is 12:00)

What are the temperature increments? What would the temperature be at 1 mark after 210? 225 or 235? Is that an acceptable temperature under a load? It doesn't ever pass that, the Jeep has never had a boil over, nor has it ever actually overheated.

Is it possible that the sensor inside the housing is +/- 10-15°?

Or are we talking about another sensor?
 
For highway driving, I would expect temperatures to remain right around 210F unless you are in the desert, i.e. I-8 between El Centro and San Diego or I-17 between Phoenix and Flagstaff. You may very well have poor airflow (condenser, radiator) or blocked passages in your radiator.

The cheapest OK radiators are $100 are the Spectra radiators from Auto Zone, NAPA, Advance, etc. I have hard good things about the Mopar HD.

I too had the Dexcool syndrome. I am not sure who introduced it into the Jeep. The crap is almost impossible to get rid of it. It is "easier" to replace all the hoses and radiator and change the condenser while you are at it. Change the fan clutch while you are at it, unless you are sure it is recent. Performance degrades over time. Then you have "factory new" cooling system performance and your temp gauge will probably stick just below 210F for nearly all highway driving.
 
The orange long life coolant was started in 99 IIRC. It's not dexcool. It was certainly crap though. Every one that wasn't changed out in 3 years turned brown and gunky. I've certainly flushed my fair share when I worked at the dealer.

I highly recommend the Mopar HD radiator found in 99 and up and it fits any HO 4.0 xj. search the modified section and you can find the part number. it's over $200 but well worth the coin. Most OE XJ radiators lasted 100k and many went 200k miles. No reason not to install another IMPO.

Ditto on the fan clutch.
 
Digger87xj said:
I highly recommend the Mopar HD radiator found in 99 and up and it fits any HO 4.0 xj. search the modified section and you can find the part number. it's over $200 but well worth the coin. QUOTE]

As listed before:
Mopar 52080104AC
Click to expand...
 
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