Jeep sounds

[MarkC]

My 96 Cherokee has always run flawlessly. It has 88K on it, I change the oil every 3k, using Castrol GTX 10W30, and either PureOne or Napa Gold filters.
Lately, I've noticed that after being driven a while, the engine has a faint knocking sound at idle. You can barely hear it, but I know it hasn't always been there. I can't tell if it increases in frequency when the rpms go up because the engine noise drowns it out, or, for all I know, it stops.
Never hear it at startup, only after driving a while at operating temp.
This engine consumes no oil at all, and the coolant level stays constant.
Since the noise seems to originate from the front of the engine bay, I'm thinking maybe the water pump is having issues. My old Mustang used to thump and knock like this, although much louder and stronger, and it was indeed the water pump.
Temperature is normal, just as always.
Anybody have any ideas?
Thanks

[ October 03, 2003, 01:51 PM: Message edited by: MarkC ]

 

[Ed]

Sounds like injector noise to me. Jeep engines were never known for being quiet.

 

[dickwells]

One thing you can do is try it with no load and with a load (either from clutch or auto trans) If it gets louder under load I think it points to the mains, it it gets quieter it points to the rods. In your case it may just be piston slap or some such. Regards, RW

 

[widman]

Define "knock". Before you see piston slap or anything like that you should see oil consumption.
Could it be "ticking"? I had to replace my lifters at about 75,000 miles on my 93 GCL. I quieted it down for a while with 20w50 before I could get the lifters. Might be a case for AutoRx to clean it up a bit.
A definite knock I had was a broken engine mount. Allowed the engine to vibrate against the frame. It's a lousy hollow design that gives out easily. I took my broken ones to the local tire re-treader and had them filled solid.

 

[cousincletus]

The first thing you should do is determine if the knocking is an accessory or not. Remove the belt and see if the noise goes away. My first guess is a water pump going bad, since you said that it's a knocking, not a ticking noise.

 

[MarkC]

Thanks, gentlemen.
The sound is not a ticking, and not really a knock, more of a dull thumping that's very faint. Since I posted this, naturally it stopped.
In cold weather, I do have a ticking, that drove me batty untril I relaized it's a solenoid.
I tend to think this is the water pump.
But I'm not seeing any loss of coolant, or oil, or anything else.

 

[cousincletus]

You won't necessarily see a loss of antifreeze when the water pump is going bad. The bearing seems to get a lot of noise before completely failing. See if there is any play in the shaft. There shouldn't be any. If there is, then replace the water pump.

 

[jeepzj]

MarkC, the purge solenoid on the Evap system on my Jeep makes a soft thump sound that is normal. Mine is located along the drivers side firewall next to the airbox. It has a green cap on it with a sticker that says "EVAP". It can only be heard at idle with the radio off and windows up. Starts to thump as the engine gets warm. So in the morning when I first start up the engine you don't hear it. 5 minutes later it starts making the noise because the engine temp start to climb.

 

[MarkC]

Yeah, I've had that sound in cool weather, comes from exactly the same place, as only as the engine warms, then it goes away.
The current sound seems to originate from the front of the engine bay, and only when the engine has been hot for a god while. Since I posted this message, it hasn't recurred.