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Water pump going south?


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9 replies to this topic

#1 hohieu

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Posted 11 May 2008 - 10:13 PM

My brother-in-law overheated our '91 XJ at around 195K miles -- a leaky bypass hose causing loss of coolant and the radiator to melt.

Now at 205K miles, I hear a whistling that changes pitch with engine speed. I suspected the water pump was going south and took off the belt to confirm and also find a tiny bit of in & out play in the water pump pulley. I replaced the idler pulley, which was leaking grease and had some play lateral play, but all other accessory pulleys had no play or roughness. The whistling is unchanged, and I should add that the engine idles and performs normally otherwise.

Does this confirm my suspicions?

Any other thoughts?

#2 Nug

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Posted 12 May 2008 - 10:51 AM

If you suspect other accessories, you could remove the belts going to them, one at a time, and run the engine. This can help isolate the noise.

#3 hohieu

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Posted 12 May 2008 - 11:28 AM

Wish I could. Unlike our Subes which have two accesory belts, these 4.0 L straight six have one serpentine belt driving all accessories.

#4 Nug

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Posted 13 May 2008 - 06:48 PM

While play in a water pump isn't ideal, I wouldn't condemn it if it spun smoothly without roughness.

I've noticed the distributors in some 4.0 jeeps squeak, and sometimes wobble like they are loose. Might want to glance at it.

Thermostatic fan clutch may also be dying. usually they roar or knock when they start seizing, but you never know.

#5 nipper

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Posted 13 May 2008 - 07:23 PM

Spray water from a spray bottle on the individual parts. If its a bearing it should change pitch.

Whistling noise usually is an alt.


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#6 hohieu

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Posted 14 May 2008 - 01:30 PM

I should add that it's definitely a high pitched, faint, whistle and not a belt screech or chirp. It's most noticeable due to the change in pitch during accelearation or deceleration between idle (@750 rpm) up to about 2000 rpm. If I hold it at 1200 rpm or so, it's barely audible, and bove 2000 rpm, it's inaudible, perhaps because engine noise drowns it out.

Really hard to pinpoint the noise. I was out there with some tubing and put it up to all the accessories and couldn't locate the noise. I sprayed water around the vacuum hoses to check for leaks, even though it runs and idles perfectly fine. I also sprayed the accessory pulleys as suggested by Nipper with no effect.

While play in a water pump isn't ideal, I wouldn't condemn it if it spun smoothly without roughness.


It spins smoothly & freely, perhaps a little too freely as compared to a new pump. We acquired the this car from my mother-in-law, who was the original owner, and she had no record of the WP ever having been replaced. Her records may be incomplete, but the oxidation on the water pump is consitent with that on the adjacent aluminum power steering bracket. If it's indeed the original pump, after 205K miles/17 years, it might not be a bad idea to swap in a new one for peace of mind.

I've noticed the distributors in some 4.0 jeeps squeak, and sometimes wobble like they are loose. Might want to glance at it.


Ah yes, I forgot to mention that this is the 4.0L l-6 egine. The distributor looks good.

Thermostatic fan clutch may also be dying. usually they roar or knock when they start seizing, but you never know.


I'll check this out but doubt it's the problem. The whistling isn't very loud at all.

Nipper, I hope you're wrong about the alternator, but I'll check the pulley again when I take the belt off.

#7 hohieu

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Posted 20 May 2008 - 07:58 AM

Well, I decided to go ahead and replace the H20 pump and t-stat. After running some prestone super cleaner through the system for the past week, I removed the old pump, and it really was on its way out. It hadn't started weeping, but the play in the bearing caused the stamped impeller to wear grooves into pump housing, similar to grooves on a poorly worn brake rotor. I more or less confirmed that the old pump is the original OEM pump. Along with reasons previously stated, the manufacturing info. casting on my old pump also matched that on the pump pictured in my Haynes manual.

The good news is that the cooling system channels appeared to be in great shape with almost no corrosion.

The bad news is that the whistling is still present, and as Nipper inferred, it does appear that it's my alternator. The noise is still faint so I'll just wait until its starts to really scream or until the voltage gauge on the dash starts to dip below normal levels.

Thanks for all your input.

#8 hohieu

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Posted 22 May 2008 - 11:52 AM

When you have multiple things going all at once, not uncommon after an overheating, it's hard to pinpoint the culprit.

Funny thing is that I did hear some intermittent faint scraping noises that would usually arise when I turned on the AC and and then subside. I feared that the compressor was starting to punk out, but I now realize that it was the extra load on the belt that caused the water pump impeller to scrape against the housing.

I've attached a picture of the old pump that shows the circular scrape marks on the housing -- still pretty incredible to me that the original pump lasted that long. I wonder how much longer it might have gone if not for the overheating.

Attached Files



#9 nipper

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Posted 22 May 2008 - 11:55 AM

Usually the design parameter is around 100-110,000 miles, but they are so over built for what they do (and have to be) they usually last 50-70% longer, even more if the fluid is changed regularly. I would think it would have lasted till the first traffic jam in august with the mother in law in the car.

:cool:

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#10 hohieu

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Posted 23 May 2008 - 10:58 AM

I doubt that she regularly replaced the coolant (nor any of the other fluids) so it's a real credit to this particular water pump. It's good though that she did have the engine oil replaced regularly.

One improvement to the new pump is the placement of the weep hole. On the original pump, it's located on the bottom, blocked from view by the crank pulley, and requiring you to get under the car to trace the leak. On the new pump, it's right on top and can be seen standing in front of the hood.

In my 10k miles of ownersphip, I've replaced all the fluids a couple of times (ATF, transfer case fuild, front & rear differentials, brake fluid) and now the coolant. The rear differential oil was black when I first drained it -- guess that's how gear oil gets after 200k miles.

After new front & rear crank shaft seals, oil pan gasket, valve cover gasket, and some other odds and ends, the car leaks nothing, consumes perhaps 1/2 qts. of oil/3k miles, and it still gets the EPA estimated 20 to 21 mpg on the highway. I'm very impressed by these earlier Cherokee models.

When you acquire an older car like this, it always takes a while to find and fix all the problems, none of which were serious. In addition to the water pump and t-stat, I've also replaced or rebuilt the following over the past year or so:

- shocks with KYB GR-2s
- steering stablizer
- front sway bar end links
- vehicle speed sensor
- bulbs and fuses
- rebuilt front brake calipers (brakes were acutally smoking due seized
front caliper)
- rebuilt the neutral safety switch

After a new alternator, this car could go the distance...




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