What could this be?

[MarkC]

For a couple of months, I hear a faint thumping or knocking noise on the driver's side of my Cherokee's 4.0. Nothing big, and not very loud.
I was thinking the water pump might be thinking about giving it up, but when I pop the hood and take a peek, the pulley and belt seem to be doing their thing properly, and I can't hear the noise from out there, only from inside the Jeep.
It may just be one of the 4.0's normal sounds that I haven't noticed before. Any ideas?
The cooling system works fine, no lose of coolant, no overheating.

 

[Gary Allan]

You've gotta gives us more than that

Constant ..increases with the speed of the engine..only when going down the road ..or in gear ..or whatever.


"you can't just say my cat died" type thing.

The 4.0 and the 2.5 are LOUD engines to start off with. Heck have mine idling YOU KNOW IT. You don't even hear the new stuff (asian). A whole bunch of valve train noise.

 

[MolaKule]

When idling, going down the road at high speed, low speed? Turning slowly, turning fast, on acceleration, deceleration?

How old is the vehicle, how many miles?

I'd look at the shocks, struts, steering knuckles, ball joints, etc., first if it's an older vehicle. When was the last time it had a chassis lube?

Like Gary said, man, you gotta gives us more than this. Our crystal balls get hazy with stuff like this!

 

[Mazatrol]

Exhaust leak??......like said above...a little more detail would be helpful.

 

[Gary Allan]

quote:

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Exhaust leak

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Glad you said that. The 4.0 is prone to having the manifold crack. There's a proposed class action against DC over it. That would be on the drivers side as well. It's not a typical exhaust leak either ...it's not all that loud (typically).

See (if this is it) ..your cystalball is doin' just fine

Pass that buffer over to Molakule

 

[MarkC]

Almost 98K on it. I hear it only at idle, and not always; mostly sfter driving a ways, and after the engine is warmed up. The sound reminds me of the sound a water pump makes when it's getting worn, but I don't think that's it. It's not noticeable while driving, and as I said, I can't hear it when I'm outside the cabin looking under the hood.

 

[tpi]

If you think it accessory noise such as water pump etc. on newer cars it is easy to temporarily disconect the serpentine belt for a quick check. You can safely run the engine at idle for a brief time without the pump turning, listening for the noise. When the belt tension is off (engine off) it is easier to spot loose bearings by rocking the pulleys back and forth.

Is the noise rythmic or random? Most of the water pumps I've heard with loose bearings will make a random rattle, not a rythmic tap tap tap. If the pump is loose enough to rattle you can usually rock the fan back and forth and see the play on the water pump shaft. Idler pulleys are often another source of bearing noise or rattle.

[ August 02, 2004, 11:29 AM: Message edited by: tpi ]

 

[Mazatrol]

Do you notice it a little more during moderate to hard acceleration??....with the engine fully warmed.

 

[MarkC]

I can't notice it at all except when idling. Even then, I have to be sitting inside to hear it. If I rev the engine a bit, to see if the frequency increases, I cna't hear it.

 

[MolaKule]

WHat jeepzj said.

FWIW, I had a similar noise one time on a '92 Suburban. It was the serpentine belt Idler pulley; bearing was going out and it had flat spots on it that did this "ticka, ticka, ticka" only at idle.

 

[MarkC]

Thanks, gentlemen. I'll check those things, although the washer reservoir on mine is on the passenger side.
I appreciate the input.

 

[Virtuoso]

jeepzj might be right - My old Avenger did the same thing. Only loud enough to hear at idle, but I had to be outside of the car to hear it. A very light muffled 'thud thud thud' sound.

 

[jeepzj]

Hey MarkC if the thumping sound is what I think it is you have nothing to worry about. It's normal. When you hear the noise again, keep the engine running at idle and open the hood. Place your finger on the EVAP purge solenoid (I think that's the name). Should have a green sticker on it. Anyway it's located along the driver's side inner fender next to the washer fluid resevoir on the 4.0. Touch it and you'll feel it thumping. That's the noise. You should only be able to hear it during idle inside the cabin after the engine has warmed up a bit. I don't think you'll be able to hear it first thing in the mornig while the engine has just started. I believe the EVAP purge activates as the engine starts to get warmed up. Check it out and let us know.