Just recently, my belt starting singing it's love song. It's only when I'm hitting the gas or under load. Could it be the belt or maybe a pulley? What should I check. I've never had to replace one and I feel like a noob right now.

 

Could be the tensioner/idler pulley. For the longest time I had a very light, raspy whirring sound that I always thought was something internal...turned out it was the pulley going bad. I only replaced it because I had to do the tensioner bolt and just figured I'd do the pulley, too.

Just take the tension off it and turn it by hand to see if there's any crunchiness. Mine would move like a ratchet; the bearings were almost completely shot.

 

How many miles on it? Inspect it with a good light....does it have excessive cracking or glazing? Is it properly tensioned?

Any doubt, replace it. I recommend the Goodyear Gatorback. Stay away from el-cheapo belts. And be sure it is properly tensioned as the belt on the 4.0 needs to be pretty snug to stay quiet. You may have to snug it up after you run it for a few days.

 

It's got 200k. The belt looks pretty shiny, but no cracks at all. I bought a belt from Napa us in case and I think it was a Goodyear if I remember corectly.

 

Shiny as in glazed? You want the rubber to look like it is "matte" finished, smooth with no cracks or striations in the rubber.





EDIT:

Pull the belt off if in doubt, clean all the pulleys and spin them to see if you can hear for any bearing noise. I have a pulley going out that I need to change this weekend, fingers crossed it's the idler pulley and not the alternator or power steering pump...

 

is you belt squealing or is a pulley chirping?

you may just need to remove the belt and scrub it with soap and water and reinstall.

but while it's off, spin each pulley and listen for a bad bearing.

 

No chirping. Just squealing and it's not constant. Once it's warmed up, the squeal is gone.

 

Definitely not matte at all. I'm going to do as suggested and pull the belt and check the pulleys. While the belt is off I'm replacing it.

 

As you prolly remember, I'm the fellow Marylander doing the extensive rebuild of my son's XJ and as part of that I opted to replace the serpentine belt. I bought the Dayco brand from Advance and its driving me crazy trying to get it to stop squealing/chirping. As part of the coolant system rehab, I have recently replaced the water pump (slagged), ps pump (leaky), alternator (seized), clutch fan (slacking) and tensioner/idler (hoping that was the problem) . The OLD belt wasn't squealing or cracked but was starting to glaze a bit. I'm tempted to put the old one back on at this point. If I do that at least I'll know if I should be chasing a pulley. I was going to snag a Gatorback but I don't think anyone local stocks them. Good luck.

 

x2 on the Gatorback. Quiet and solid.

Also invest in a cricket (Gates Belt Tension Gauge)

Best $15 you will spend when you have a squealing belt. tjwalker is right, the 4.0's need a VERY snug belt.

 

Not too snug though...I just broke the nut/block thing that the bolt goes into, and it was a dealership part. Split right along the threads. Looked kind of cheap, like it was cast.

Got a new one from amazon and it looks like it was actually machined instead of cast. Picked up the tension gauge as well.

 

Be sure to check your harmonic balancer! My belt was squeaking and I kept tightening it for a while until it started loosing strips. The balancer was seperating and walking into the front cover.

Luckily the timing cover is the same on the 4.0 and 2.5L.

 

Check the fan too. I thought my belt was squealing under hard acceleration. Turns out the fan clutch was worn out and making noise. Watch the fan while you rev the motor. If the blade moves in and out, clutch is gone. Also can grab fan blade (motor off) and push forward and back, shouldn't move much. Mine was moving about 3/8".