Question about 1999 Jeep Grand Cherokee

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99 Jeep Grand Cherokee Ltd. 4.0 ltr overheats and we changed the thermostat, water pump, temp sensor, air intake sensor, electric cooling fan relay, cooling fan motor, and fuse. Motor turn on by a scanner a buddy had that's better then my obd, So it can turn on but not on its own. I also am having trouble with the heat, It can make heat when it is on inner air circulation but when I take it off the air gets cold. We are winter here and can get to 35 below. So I can only use defrost briefly before I have to turn it on floor or interior air to get the inner air circulation to reheat the jeep.

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  • mz_pepper Dec 31, 2010

    The cooling fan is not turning on. We can't figure out why. We had a friend check it with a scanner and he turned the fan on with it but nothing we do can let it turn on like it should.

  • mz_pepper Dec 31, 2010

    The cooling fan wont turn on. It will with my buddys scanner but not as it should. So he said it was not the wiring.

  • mz_pepper Dec 31, 2010

    We read that here and changed the thermostat sensor, then the relay under the headlight, the intake air temp sensor, changed the thermostat, fuse, water pump and the fan motor. All ideas we got from this site or our mechanic buddy. He hooked up a scanner and was able to turn it on with the scanner but we still cant get the fan on or get the heat warm while not on the inner air circulation mode. Dont know if it is all tied together or not. We are at the point of changing the computer. But not sure about it. Seems like there is nothing more to do then to rig a toggle switch or put on a mechanical clutch fan. Was hoping we can fix it hand have it the way it was supposed to be.

  • mz_pepper Dec 31, 2010

    We changed the thermostat temp sensor, relay under the headlight, air intake sensor, thermostat, water pump, fan motor, and fuse. We had a mechanic buddy who ran it on a scanner and he was able to turn it on with the scanner. The scanner and the OBD said the sensor was still out even thought we changed it. And it still overheats while idling.
    Also noticed that it has a delay on the airflow when you switch from hi all the way down to hi on the top of the dial and sometimes it wont kick in and I will have to go back to hi on the bottom to get it going. Dont know if this is something to do with the heat. I am not sure if there is a actuator or something making the heat a problem for the interior.

  • mz_pepper Jan 01, 2011

    I think this is the solution

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Hi and welcome to FixYa!
Jeep still overheats? If it does then the problem can be on the cylinder head gasket. Worn out gasket can result to overheating. Have it replaced.

Hope this helps and thank you for using FixYa! Have a good one!

Posted on Dec 31, 2010

  • dj_relly999
    dj_relly999 Dec 31, 2010

    If it's not the wiring then it must be sensor that triggers the fan when the engine is hot. If it's worn out the fan will not automatically turn.

  • dj_relly999
    dj_relly999 Jan 01, 2011

    Hi! That's what I'm suspecting. The car's computer can be failing that's why the electrical is acting up. If I am to ask, I'll go with the computer.

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1 Answer

I have a 99 grand cherokee limited 4.7 that overheats when on the hwy


Sounds perfect to me. The fan sound is normal for a clutch fan. The temps are just not too high at all. Remember, the system has two main points that make the temp okay: Coolant (in the right amount) and PRESSURE. Both seriously raise the boiling point.

At even higher temperatures, Eventually, you should hear the fan kick in, as loud as when cold..This REALLY moves air through the rad and should curtail any overheat.

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Although the 4 cylinder is too underpowered to have air conditioning in my opinion, it still shouldn't overheat within 10 minutes unless something is wrong. If your Jeep doesn' not overheat when you are driving WITHOUT AC on then your compressor might have a problem and causing the engine to work too hard to turn it.

But if it overheats without the AC on, then the first thing you need to do is check the cooling fan and see if it operates! There has been a lot of problems with the cooling fan relay on this model. If that isn't it, then move to changing the thermostat and checking the water pump.

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There is the coolant sensor that tells the computer the temp,and the computer sends a signal to the cooling fan relays,and the relay turns the cooling fans on,and off,if the system is low on coolant,or has air in the cooling system,then the cooling fans would not come on,or the sensor is bad,if this was at all helpful,please rate,thank you.

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1 Answer

It overheats thermostat was replaced and cooling temp sensor what else could it be


Bad water pump. Clogged radiator passages. Air pocket in the cooling system. Blown head gasket.

Jul 29, 2010 | 1999 Jeep Grand Cherokee

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2004 jeep grand cherokee overheating


check the thermostat or your radiator might be stopped up

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1 Answer

2000 v6 4.0 jeep grand cherokee ltd overheating problem,anti freeze over flowing out of over flow tube


Several causes for that. First, check for any external leaks. Check engine oil for any coolant intrusion and check tailpipe for excessive smoke.(possible head gasket problem)
Main common causes of overheat are lack of flow: bad thermostat, (after an overheat, thermostats become unreliable replace it as "routine" they are inexpensive.) internally or externally obstructed radiator (internal, flush or replace, external, clean leaves bugs etc from outside front of radiator.) A radiator that takes a long time to fill generally is internally blocked. Bad cooling fan, fan sensor or relay. (make sure electric fan comes on when engine reaches or is just above normal temp...If not, hot wire fan motor to battery....replace if it does not run. find and check
relay if there is no power and ground at the fan plug harness when fan
should be on...relay may be in power distribution center or below right front headlight, best accessed from below. If no ground signal at relay from the computer, check the temp sender. (sender sends info to computer which sends ground to relay that sends power to fan motor)
If water pump is not leaking or noisy, leave it alone...they will pump even when the seal and bearing are horribly bad...there is no "secret stuff" in there.
It also won't hurt to check the clutch fan if you have one....it should spin free when cold and offer some resistance when hot. Pretty rare they fail but they can.
Any questions just ask
good luck!

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2 Answers

Overheating while Eating


Bad themostat, dirty radiator (the front of it), corroded interior core of the radiator, weakening water pump, bad radiator fan.....just to name a few. More than likely? Low antifreeze level, or the thermostat.

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1 Answer

Over heating when sitting at idle for a short while


It sounds like it may be your electric cooling fan. When the car is sitting idling does the fan behind the radiator ever come on? If not then this is your problem. Your car doesn't overheat when it moving because you're passing air through the radiator with the movement of the car. The problem could be the fan itself, the fan relay, or a temperature sensor.

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3 Answers

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Three possible solutions:

1. Bad Thermostat

2. Fan Relay (most likely)

3. Bad Fan

When the GC reaches a temp of 180 Deg. F the fan relay sends a signal to the fan to turn on, once the temp lowers (around 155 Deg. F) the relay turns off the fan, and so the cycle continues. If the relay is bad there will be no signal to the fan to run. While you are driving your vehicle there is ambient air moving thru the radiator, cooling the engine, but once you encounter slow/heavy traffic or stop there is no air moving and the temp goes up, the fan will not kick in and the vehicle will overheat.

If the fan motor is not working the same will happen, but a more expensive fix, as the motor comes with the fan.

If the Thermostat is stuck in the open position, the water travels to fast in the engine and heat exchanging is not an efficient process, therefore the vehicle might overheat when stopped or in slow traffic.

Mar 31, 2009 | 2001 Jeep Grand Cherokee

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