91 cherokee overheats at high speeds - JeepForum.com

 
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post #1 of 8 Old 04-11-2013, 11:26 AM Thread Starter
cherokeechar
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91 cherokee overheats at high speeds

So my jeep has been overheating going into the red zone at high speeds so I have been avoiding taking the freeway until it gets fixed. Heard that 4.0 l engines have issues with mineral deposits so flushed system. Thought it could be waterpump so replaced that. Just put a 4.5 in lift on it and radiator hose blew so replaced both and put a new clutch fan in as well thinking this could be it too as well as a new thermostat still having same issue... last resort I know of is replacing radiator.....?

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post #2 of 8 Old 04-11-2013, 05:09 PM
djb383
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Originally Posted by cherokeechar View Post
So my jeep has been overheating going into the red zone at high speeds so I have been avoiding taking the freeway until it gets fixed. Heard that 4.0 l engines have issues with mineral deposits so flushed system. Thought it could be waterpump so replaced that. Just put a 4.5 in lift on it and radiator hose blew so replaced both and put a new clutch fan in as well thinking this could be it too as well as a new thermostat still having same issue... last resort I know of is replacing radiator.....?
It'll all be new then........right?

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post #3 of 8 Old 04-11-2013, 09:54 PM Thread Starter
cherokeechar
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Next week when I replace the radiator I guess it all shall be new and if that doesn't work then........ what? Just thought maybe someone knew of something I may have not thought of yet that causes this
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post #4 of 8 Old 04-11-2013, 11:33 PM
CJ7-Tim
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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. Temperature creep on the 4x4 trails, at idle, or in stop-n-go traffic points to a weak or failing mechanical fan clutch.

The most important maintenance item is to flush and refill the coolant periodically. Coolant should be replaced every 36,000 miles, or every two to 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 radiator 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 and test 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 –

www.offroaders.com/tech/engine-overheating.htm

www.familycar.com/classroom/coolingsystem.htm

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post #5 of 8 Old 04-12-2013, 04:49 PM
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Overheating at high speeds is "usually" (standard forum disclaimer) the water pump or the radiator.

Keep us posted as to whether the new radiator resolves this. Crossing my fingers that it does.....

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Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
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post #6 of 8 Old 04-22-2013, 10:28 AM Thread Starter
cherokeechar
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So finally was able to replace radiator and seems to have done the trick had to but two thermostats since when we went to replace radiator the failsafe thermo was open and decided this new thermo we put in to just be regular one one of the guys suggested those fail safe ones can do there job even if you have a pinhole of air in the line yeah to no overheating!!
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post #7 of 8 Old 04-22-2013, 11:27 PM
yankeeboy
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Just had the exact problem with my 94. I replaced everything and just like yours it was the radiator. One quick suggestion...I placed an after market temp gauge (that shows the numbers), because my car only had the blinking sensor light on the dash, which only helps in telling you once the car is already over heated. Would really recommend you adding one, if you don't have one.

"Everyday is a new opportunity. You can build on yesterday's success or put its failures behind and start over again. That's the way life is. With a new game every day. And that's the way baseball is."
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post #8 of 8 Old 04-23-2013, 01:17 AM Thread Starter
cherokeechar
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Yeah my boyfriend should have gone with his first instinct in that it was the radiator he thought he saw crystals in the water which is tell sign someone put a stop leak solution through radiator but I guess we were hoping it was something a little cheaper. Since my jeep is older has a little different setup my temp gage has numbers on it do need to replace or do something to voltage gage that's not working right since I replaced both the battery and alternator at same time .... thanks for the advice always appreciated!
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