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post #1 of 5 Old 07-27-2012, 03:40 AM Thread Starter
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Overheating Problem

I have a feeling this has probably been answered before considering I know this is a pretty common problem with Cherokees. I have a '99 Cherokee straight 6 4.0 liter and I am having a big problem with it overheating right now. I seem to get this more in the summer time which does make sense since it IS hotter outside but I have already replaced the thermostat on it and flushed the system (it has been a little while since I did this though) and I am still getting the overheating problem. I am more or less wondering if any one here has any handy tricks to help alleviate the overheating problem. If any one needs more info as to the Jeep I would be happy to provide it. I love my Jeep but the overheating problem is starting to kill me.

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post #2 of 5 Old 07-27-2012, 07:18 AM
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Check the fan clutch and the water pump may need to be replaced
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post #3 of 5 Old 07-27-2012, 10:27 AM
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If the radiator has not been replaced, put a new radiator in and make sure there is a new pressure cap. I usually do that and new hoses & water pump & idler pully, every 5 years or 200,00 KM. (120,000 miles). Radiators are a disposable item since copper is not used anymore.
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post #4 of 5 Old 07-27-2012, 06:44 PM
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Overheating cooling system

Overheating can be caused by anything that decreases the cooling system’s ability to absorb, transport, and dissipate heat, such as a low coolant level, loss of coolant (through internal or external leaks), poor heat conductivity inside the engine because of accumulated mineral deposits in the water jackets or radiator, a defective thermostat that doesn’t open, poor airflow through the radiator, a slipping fan clutch, an inoperative electric cooling fan, a collapsed lower radiator hose, an eroded or loose water pump impeller or even a defective radiator cap.

The cooling system is a group of related parts that depend on proper function from each of its component parts to keep the engine cool. Service the cooling system and replace any under-performing or suspected weak parts. Any component part of the cooling system that is not fully doing its job will stress the others and your cooling system will overheat. The most important maintenance item is to flush and refill the coolant periodically. Coolant should be replaced every 36,000 miles or every three years. Anti-freeze has a number of additives that are designed to prevent corrosion in the cooling system, but they have a limited life span. The corrosion causes scale that eventually builds up and begins to clog the thin flat tubes in the radiator and heater core, causing the engine to eventually overheat.

-Use a flushing/cleaning solution and then drain and fill the radiator with a fresh 50/50 coolant and water mix.
With a neglected cooling system you may have to flush several times.
-Inspect the radiator for mud/bugs/grass clogging the outside and mineral deposits clogging the inside. Clean or replace as needed.
-Replace the thermostat with a STANT or Robertshaw 195* thermostat. Cheap thermostats are cheap for a reason.
-Replace the radiator cap if your Jeep has one. An old worn out cap will allow boil overs and/or allow the coolant flash over into to steam. You will see the coolant temps suddenly jump from 210* to the Red Zone and back to 210* if your radiator cap is weak.
-Inspect/test or replace the mechanical fan clutch. A worn fan clutch will allow temperature creep at stoplights, in heavy traffic, and on the 4x4 trails. A fan clutch that “looks” OK is not the same as working OK.

-Inspect the electric cooling fan and the fan relay. Apply 12 volts and make sure the fan runs. Exchange the cooling fan relay with one of the others similar relays. Confirm that the e-fan starts when engine temps reach 215-218*. Repair or replace the fan or relay as needed.
-Inspect/test or replace the coolant temperature sensor that activates the e-fan.
-Replace the water pump. The pumping fins can deteriorate over time and the pump will not flow enough coolant to keep the temps under control.
-Inspect/replace the radiator hoses. Make sure the coiled wire is installed in the lower hose.

If you have covered all the points listed above and still have overheating issues, inspect the head for cracks and head gasket for leaks. Exhaust gasses entering the coolant can raise the temperature of the coolant or cause steam pockets in the coolant that will temporarily block the flow of coolant

Read more about cooling systems here –




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post #5 of 5 Old 07-27-2012, 10:16 PM
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CJ7-tim did a great post. I did remember one oddball thing you need to watch for. The waterpumps were built with left hand and right hand rotation impellers (marked with a stamp), depending on your belt routing. You may want to verify the impeller stamp if the pump gets taken off.
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Fan clutch , overheating , radiator , radiator cap , thermostat , water pump

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