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  #1  
Old July 15th, 2005, 15:50
90Pioneer 90Pioneer is offline
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Does this sound like a bad radiator or water pump?

I have a '96 XJ with 77k miles. All week it's been in the 90+ degrees. Normally the Jeep stays cool and runs great. Well today it started overheating, with AC on and off. The temp will even climb a bit at highway speeds. It's been pretty much over heating at all speeds today (hasnt gotten to the red though).

Putting it in park or neutral and holding at 1700ish rpms brings the temp back down, but climbs up quickly once I've stopped. Heater trick also cools her down.

Does it sound like my water pump is not flowing enough or is my radiator clogged? I serviced the coolant about 5k miles ago. My fan clutch seems tight and appears to be working properly.

How complicated is it to change out the radiator?
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Old July 15th, 2005, 17:05
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Re: Does this sound like a bad radiator or water pump?

Is your electric fan kicking on?

Usually, when you can bring the temperature down by blipping the throttle at lights, it's a good sign that the radiator is working, but flow is suffering somehow. Here's a few things to check...

1) Just for fun - grab the lower hose and squeeze - you shouldn't be able to. There's supposed to be a metal coil in there to keep the hose from collapsing under suction. You probably aren't having this problem, but check anyhow, and make a note of it...

2) How old is the coolant? There are corrosion inhibitors that break down with age, and one of the first things to corrode is the water pump impeller. This will reduce pump flow capacity, and when you blip the throttle or are at cruise RPM the higher flow hides the condition. You might need to check the water pump (I've seen cases in various vehicles where the impeller was GONE - corroded entirely away...)

3) How do you check the fan clutch? While the test I tell everyone about isn't 100% reliable, it's pretty good. It's also a fair bet that, if it's more than 5 years old, it's shot. If you're sure it's over 5 years old - or have no idea how old it is - change it. I tend to sign and date mine when I install them, so I can tell later (you think I can keep all the maintenance lists for several vehicles in my head? Are you crazy? Why do you think they make engravers and letter stamps?) Even if the fan clutch is shot, the fan will turn a little faster when you blip the throttle, and the increase in coolant flow will also help to depress temperature.

4) Since you are getting cooling at speed, we can safely assume that the thermostat is in good condition. Remember - one single overheat and it's toast!

HTH, YMMV

5-90
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  #3  
Old July 16th, 2005, 06:48
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Re: Does this sound like a bad radiator or water pump?

Good suggestion about marking a part(s) install date, why didn't I think of that...DUH.

Last edited by dizzymac; July 16th, 2005 at 06:48. Reason: error
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Old July 16th, 2005, 09:07
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Re: Does this sound like a bad radiator or water pump?

Quote:
Originally Posted by 5-90
2) How old is the coolant? There are corrosion inhibitors that break down with age, and one of the first things to corrode is the water pump impeller. This will reduce pump flow capacity, and when you blip the throttle or are at cruise RPM the higher flow hides the condition. You might need to check the water pump (I've seen cases in various vehicles where the impeller was GONE - corroded entirely away...)


5-90
I know that there have been some cases of WP impellers getting eaten away by corrosion. One guy even posted pics of such on this board or JU, IIRC.

The thing that amazes me about this, tho, is that, in my 30+ years of fixing cars, I have NEVER seen a WP like that where the rest of the cooling system wasn't already total junk. (Soft, rotted radiator, hoses about ready to burst, etc.)

Most Water Pumps fail due to bearing failure, which in turn makes for weeping out the hole in the bearing support.

I guess what I am saying in a roundabout fashion is that water pump impeller failure is about the LAST thing I would look at for cooling problems.

Based on experience, my rule of thumb for XJ's:
overheating at road speed--check radiator flow first
overheating around town--check fan(s) operation
overheating all the time--check thermostat first, then radiator.
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  #5  
Old July 16th, 2005, 09:38
Calata Calata is offline
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Re: Does this sound like a bad radiator or water pump?

Quote:
Originally Posted by 90Pioneer
The temp will even climb a bit at highway speeds. It's been pretty much over heating at all speeds today (hasnt gotten to the red though).
Quote:
Originally Posted by 5-90
4) Since you are getting cooling at speed, we can safely assume that the thermostat is in good condition. Remember - one single overheat and it's toast!
5-90, By speed, did you mean engine speed, or traveling speed?

90Pioneer, Personally, I'd check the peep hole on the water pump first and if that's ok, I'd change the radiator. My logic is that it's even over heating at highway speeds and you also said that turning on the heater helps with your engine cooling. Turning on the heater doesn't do anything different for the water pump, but it does help take some load off the main radiator for cooling.
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Old July 16th, 2005, 10:28
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Re: Does this sound like a bad radiator or water pump?

You're getting close to 10 years old and that's when I began getting hot in summer, pulling grades, idling in traffic w/AC, etc. Between 10-15 years I played around with every "hope" in the book because I couldn't believe it was reduced radiator capacity causing this trouble. Finally swapped in a CSF 3-row and I wished I had done it from the start. Now in desert heat I can idle all day w/AC and pull grades with the temp gauge barely budging. E-fan cycles on/off nicely, no leaks, engine happy, life's good.

I'd look for signs of lime scale inside the core. That stuff seems to insulate the metal from the coolant jacket water and inhibits heat-exchanging which is what it's all about.

There are lotsa ways to check if the rad is hotter or cooler than the engine and a few other common sense things to qualify before jumping on a new rad, but based on your year, I'd strongly suspect the original rad is just not up to the job anymore.
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Old July 16th, 2005, 22:21
90Pioneer 90Pioneer is offline
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Re: Does this sound like a bad radiator or water pump?

Thanks guys. I guess I'll be getting a new radiator here soon. I'll probably throw in a Hesco water pump while I'm in there just to be safe.

I did a coolant flush with premixed distilled water prestone about 3 months ago. Replaced thermostat, thermostat housing, all houses, and the radiator cap. For a while it was almost running too cold.
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  #8  
Old July 17th, 2005, 05:43
badron badron is offline
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Re: Does this sound like a bad radiator or water pump?

At 10 year old you may have more then one problem. If the rad is 10 consider replacing it and the water pump. as well as belts clamp fan etc all at once. If you intend to keep the Jeep for some time it's a lot less work then keep going back and replacing one part at a time. Sounds like you have not over heated bad so the oil should be fine. But if you do over heat bad or a lot consider changing the oil. Check the trany fluid for color and smell to. The trany fluid is cooled by the rad (DAAAAAAAAA) It tends to over heat with the rad. So it's best to check it. Replace if in question at all.
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Old July 17th, 2005, 06:36
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Re: Does this sound like a bad radiator or water pump?

First, spend a couple of dollars and replace the radiator cap. One with a spring that is getting fatigued will cause all types of problems. It is a cheap and simple part and should be replaced every year or two anyway.
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  #10  
Old July 17th, 2005, 14:13
90Pioneer 90Pioneer is offline
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Re: Does this sound like a bad radiator or water pump?

I replaced the radiator cap, hoses, etc 3 months ago. All parts were from the dealer. Today I picked up a bottle of water wetter, abd I poured it into the radiator through the upper hose. Hopefully this will make some difference.

I'm looking into having a stoker built, so I may hold off replacing anything until I decide what I want to do, and who's going to build it.

I'm running Amsoil 5w40 that was changed less than 1,000 miles ago. The temp maybe got up to 235-240. I hope that would not warrent an oil change.
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