I started hearing this "thump thump thump" sound coming from under the hood today. Turns out the serpentine belt is starting to come apart. What would be the most likely cause of it's premature death?

I asked a few people was told they should normally last 30-40K. Does that sound about right?

 

Go to the passenger's side of the truck. With the hood open, sight (eye-ball) the serpentine belt and align it with all the pulleys.

-> See if the belt tensioner pulley is crooked to the others and belt. It's quite normal and is a result of the rubber component of the tensioner aging and getting soft. With the tensioner pulley tracking wrong, it tends to steer the belt off the other pulleys and has it get chewed-up

You need to get a new tensioner assembly.

 

Is this a part I need to get from Cummins or Dodge or Napa? Would you happen to know any parts numbers for it off the top of your head?

 

all aftermarket stores sell the tensioner, big difference in prices, 4bt from napa 126. autozone 63. cummins part number is on the tensioner.

 

You want a Dayco tensioner. It's OEM.

 

The dayco is also lighter and a much better designed piece than a gates or similar. It should be cheaper also.

 

Dayco# is 89219, right?

 

Depends on where you bought your belt if tensioner is any good and how the pulleys are lined up. Bearing in water pump any good also p/s pump or ac compressor going out,