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Overheat at idle.

CJ96xj

NAXJA Forum User
Location
Bel Air, MD
I have a 96 XJ 4.0L. I have a problem when I idle, the temp creeps up to the 240-245 mark. The clutch fan does not seem bad, no wobble/excessive movement, but am not totally sure. The electric fan only comes on with the A/C or defroster, not at 220. Could it be the CTS? the gauge seems correct though. I've checked the forums but cannot find a condition like this.

Thanks
 
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The electric fan should come on around 220 to compliment the mechanical fan. You could have a bad temp switch for the fan, The relay and fuse should be good because it works with the ac/defrost. Check out a manual or wiring diagram/component locator to find this switch, usually it will be open until it reaches temp then closes letting power or ground through turning the fan on. Until you find out what is causing your problem turn your defrost on at idle to keep the temp down.
 
Yup, need to ensure that your e-fan is working properly. That is job #1.

After that, the #1 cause of temp creep at idle is the fan clutch. Hard to tell for sure if they are good or not. They don't last forever, are cheap and easy to install.
 
The engine, at idle, should not be overheating with just the mechanical fan BY ITSELF as long as no a/c is running.

Sounds like a weak/failing mechanical fan clutch.

Try raising the RPMs when it starts to heat up at idle, the temp drops it is the fan clutch.

FSM fan clutch test:

"The cooling system must be in good condition prior to performing the test outlined below to ensure against excessively high coolant temperature.

CAUTION: Ensure that there is adequate fan blade clearance before drilling.
(1) Drill a 3.18 mm (1/8 in) diameter hole in the top center of the fan shroud.
(2) Insert a dial thermometer -18 degree to 105 degree C (0 degree to 220 degree F) with an 8 inch stem, or equivalent, through the hole in the shroud. Ensure that there is adequate clearance from the fan blades.
(3) Connect a tachometer and an engine ignition timing light (to be used as a strobe light).
(4) Block the air flow through the radiator by securing a sheet of plastic in front of the radiator (or air conditioning condenser). Use tape a the top to secure the plastic and ensure that the air flow is blocked.
(5) Ensure that the air conditioner, if equipped, is turned off.
WARNING: USE EXTREME CAUTION WHEN THE ENGINE IS OPERATING. DO NOT STAND IN DIRECT LINE WITH THE FAN. DO NOT PUT YOUR HANDS NEAR THE PULLEYS, BELTS, OR FAN. DO NOT WEAR LOOSE CLOTHING.
(6) Start the engine and operate at 2400 rpm with the timing light (strobe light) aimed at the fan blades. Within ten minutes the air temperature (indicated on the dial thermometer) should be 88 degrees C (190 degrees F). Satisfactory operation of the fan drive requires that it engage before or at 88 degree C (190 degree F). Engagement is distinguishable by a definite increase in the flow noise. The timing light will also indicate an increase in the speed of the fan.
(7) When the air temperature reaches 88 degrees C (190 degrees F) remove the plastic sheet. Satisfactory operation of the viscous fan requires the air temperature to drop 20 degrees F (11 degrees C) or more. A definite decrease of audible fan air flow noise should be noticed. Replace defective fan assemblies."
 
I think i may have fixed it partially. i changed the CTS and now the fan turns on past 210 like 215, and it runs around that. But I did notice while running, the clutch fan wobbles a little, not to extreme. i may replace it just as preventive maintenance.
 
Yeah, that would be the 97-98 ZJ HD upgrade.
 
When was the last time you changed out the thermostat?
I had one that was bad this summer. Seems like they're good
for maybe 2 years. Good preventive maintinance yould dictate
changing it out yearly.
 
I just replaced the clutch, temp problem all better, but broke the shroud in the process.:banghead: now to find a new one to somehow get past the fan...
 
I just replaced the clutch, temp problem all better, but broke the shroud in the process.:banghead: now to find a new one to somehow get past the fan...

I think someone posted up they were dirt cheap at rockauto.com recently.
 
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