1999 Jeep Cherokee 4.0. 4WD, 4 speed auto, been running great. 165,000 on the clock, changed the oil about 700 miles ago. Been putting new Dex3 in the transmission with drain and fills, last one was 700 miles ago as well. Oil pressure is good, around 25 at hot idle, 50-60 at highway speeds. Currently running Rotella 5W and a Purolator filter.

Jeeps been in my possession for about 12,000 miles.

Pretty much nothing done to it in the past 700 miles since the fluid changes. Drove it up into the mountains yesterday and everything was fine. Short of it going up to maybe 215F over the regular 210 or so while climbing, nothing is wrong. Green coolant when I take the radiator cap off.

Upon start up yesterday, this new noise started happening...


The scratching / metal noise is the new one. Everything else was cheeky until now.

Electric power is taking a slight dip when I use all the power windows and stereo and headlights down to 13 volts or so, and instantly goes back up. Engine was shaking a little more than usual yesterday when it was happening, so someone in Ask-A-Q said maybe the harmonic balancer, but it has no play in it. Not sure if it does even upon failure.

I took off the serpentine belt to check everything, and nothing seems to have wear on it.

-The power steering pump pulley has the slightest amount of play in it but I've had no issues with the steering. I have been replacing the fluid in there as well. Noise isn't coming from anywhere near that either.
-Idler pulley - feels okay, no resistance but spins pretty freely. Should this give a bit more resistance than that? Maybe the bearings are spun out.
-Starter - turns okay with some resistance which I imagine is normal.
-Harmonic balancer - doesn't have any play in it, pulled on it and it won't budge. No twist from broken up rubber.
-Water pump - Turns okay, no play
-AC - no clutch engaged so it spins freely, no play.

I took off the flexplate cover to check that as well. I already torqued all these flexplate bolts down again last fall, but I double checked. Nothing is loose, no broken teeth, no visible cracks.

Video of start up & power down as well as just some troubleshooting the electrical supply to see if its the alternator.

 

I don't know what that is off hand. If the problem occurs immediately on startup and suspect something belt driven, you could remove the serpentine belt and run the vehicle for a few seconds to see if it still continues. Just don't run it more than a few seconds without the water pump. I don't think you said anything about the fan blades or fan clutch. A voltage dip to 12V is not really an issue when you're running all the accessories. Your headlights probably dim when you use the power windows too. Especially when they hit the stop.

 

Regular fan is running just fine, and it wasn't hitting the balancer best I could see. That was the first thing I thought when I heard it. It sounded like something was banging around loosely. Not really sure if the e-fan ever kicks on since I don't have many issues with heating.

 

To answer your other questions, the harmonic balancer is usually two metal parts with a rubber part in between. If the rubber bond breaks, the outer section can move and grind against the timing cover. But you'd likely lose your accessories. Had that happen on a Subie once for some unknown reason. The idler pulley will spin pretty easy. Hard to know if its wobbling unless you tighten it back down and feel for play. If it spins rough then you need another.

 

Update: It was the alternator. The case cracked which was driving the brush and internal bits into themselves.

 

Glad you got it figured. Just as an aside, I know you're in cold climate but 5W viscosity is a bit too low for the 4.0 unless you just use it during freezing season. I think most folks run a minimum 10W.

 

Surely you don't run 5wt oil!