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Old 05-31-2010, 06:00 PM   #1
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Jeep Running Too Hot

My 1999 TJ keeps overheating. I do not have any leaks in the radiator, and I have already replaced the thermostat. Does anybody know what I should do or look for to find what the problem is? Thanks in advance.

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Old 05-31-2010, 06:28 PM   #2
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first things first, check the radiator really good with a flashlight and make sure it did'nt take a rock or anything to stop the flow through it.

Make sure you have the correct thermostat???

May need a flush???

Is it low on coolent?

Are you pulling a boat up hills???

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Old 05-31-2010, 07:56 PM   #3
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Check the coolant level in the radiator. Are both radiator hoses hot? Putting the heater on make any difference? Bottom radiator hose in good shape?
- dirty radiator maybe
- worn out water pump/impeller maybe.
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Old 05-31-2010, 08:05 PM   #4
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could be a fan clutch.
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Old 05-31-2010, 08:20 PM   #5
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all of the hoses look good. coolant level is good. thermostat is the right one. maybe i'll check to make sure nothing is clogging the radiator. i hope it is not the water pump
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Old 05-31-2010, 09:32 PM   #6
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when is it overheating? only while sitting or at low speeds? is it overheating while driving down the highway? (as jd said) did you check the fan to see if the fan clutch isn't working?
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Old 05-31-2010, 10:36 PM   #7
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Is it building pressure? After a drive squeeze the upper radiator hose to feel if the system has pressure in it. If there is no pressure in the system you have a leak, also if there is no pressure this means that the boiling point of the coolant is much lower than if the system was at the normal 18psi. Low pressure and boiling commonly leads to overheating.

A radiator cap can leak and you will never see a drip on the ground they just leak air pressure and a small about of coolant witch will end up in the overflow bottle.

If its building pressure I would then vote clogged radiator or bad fan clutch.
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Old 05-31-2010, 11:07 PM   #8
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while i am idling, it stays around 210 like normal, but when i am on the highway, it starts rising and after a while of running it at about 55-65 mph it goes into the red and the check gauges light comes on.
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Old 05-31-2010, 11:15 PM   #9
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Drop the coolant level down enough via the drain valve on the bottom of the radiator so you can see the top of the radiator core underneath the radiator cap. With a flashlight, look for telltale calcium deposits around the cooling channel openings indicating the radiator is becoming clogged with hard water deposits.

If you see mineral buildup inside, such deposits are caused by using tap water in the radiator instead of the required distilled water which is mineral free. At this point, I would suspect the radiator is getting clogged with those hardwater deposits. And while most radiators can be "rodded out" to get rid of such deposits, the TJ's radiator cannot be. Once it gets to that point, it can only be replaced because once it is taken apart to rod it out, it cannot be effectively resealed again since it is crimped together, not soldered.

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