Overheating w/ Cold Radiator - JeepForum.com
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post #1 of 4 Old 12-03-2013, 02:11 PM Thread Starter
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1999 XJ Cherokee 
Join Date: Dec 2013
Location: Vero Beach
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Overheating w/ Cold Radiator

I'm running out of ideas for my '99 Cherokee. It overheated on me during a highway trip a couple days ago. It had been idling a bit rough the past couple weeks (especially in reverse), but no indication it had been running hot. I pulled out the idle controller, cleaned, lubed, and replaced. Then replaced the thermostat. It sounded better when I cranked her up, so I took her for a test drive, only to overheat 20 minutes later. As it was overheating, there was a loud flapping, like a metal baseball card in a bicycle spoke, as I touched the gas. I noticed that even though steam was coming from the engine, the radiator cap was totally cold. A friend towed it home, I pulled out the water pump, which looked fine, scraped and replaced the gasket, and reattached. I then flushed the radiator, which consisted of me hosing water down where the radiator cap goes and where the top hose is connected (not sure if I'm doing that right.) Had plenty of water flowing out of the bottom hose, so I'm thinking there's no blockage. I'm just having a hard time understanding how the engine could get so hot, and the radiator be so cold. A friend suggested I get my head gasket tested, but is that my last hope?

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post #2 of 4 Old 12-03-2013, 03:01 PM
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I might look again at the water pump. See if the implelor is secure on the shaft. Other than that, maybe look at the bottom hose. If it colapses or not. See if there is a wire spring in it. Though some of the newer ones have a more ridgid hose, so they don't need the spring.
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post #3 of 4 Old 12-03-2013, 05:28 PM
Paradise XJ
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1988 MJ Comanche 
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Location: Paradise, CA
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The flapping is likely your fan hitting a broken or dislodged fan shroud OR splash shield. I'd be real surprised if it was something internal and it's really the only rotating thing that could make a noise like that. Older XJ's have a spring in the hose. Jeep discontinued them for the most part after 1990 or so. Neither of my Jeeps have them and they do fine.

As far as the overheating...how hot? Is your coolant topped up? Is it a 50/50 mix of coolant and distilled water. Is there any oil in coolant or vice versa. If all that is covered is your heater core clogged, have you flushed out the core separately? What pressure rating on your radiator cap. 13# or 16#? Does your cap have a lever on it? You have a lot of things to check before you consider a head gasket.

1990 XJ Laredo - White & Chrome
1988 MJ Pioneer - Metallic Green and Black
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post #4 of 4 Old 12-03-2013, 05:46 PM
It's the crank sensor!
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1999 XJ Cherokee 
Join Date: Nov 2007
Location: Central Minnesota
Posts: 8,850
1. Should have replaced that water pump while you had it out. New pumps are not that expensive.

2. I use only Mopar 195 degree stats. I've had plenty of issue with many of the aftermarket thermostats.

3. As you did have overheating, testing for a blown head gasket would start with a simple compression test on all cylinders. The compression spec for the 4.0 engine is 120-150 psi, with no more than a 30 psi variation between cylinders

99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
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cooling , overheating , radiator

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