I did some looking around and didn't see anything that pertained to this particular problem. My brother has a 2004 4wd hemi quad cab. It has roughly 80k on it and runs great. He bought it a couple years ago. The problem is that when the serpentine belt gets wet it starts squeaking and will not stop without replacing the belt. The belt has to get very wet, such as driving through a dip with alot of water, but will not squeak in normal raining conditions. This tells us that when water comes from underneath the truck the squeak begins. He has tried everything, belt dressing, soap, all the home remedies. He has since replaced the belt 4 times now. Once a new belt is put on, the squeak is gone. He has checked all the idlers and pulleys and they all seem to be smooth and unworn. The belts are also in good condition when he takes them off. This is a stumper to us, so i leave it to all of you. The only thing i could suggest to him was to try a different, higher quality belt. He has been buying the napa brand. any help would be greatly appreciated. thanks

 

Perhaps the tensioner needs to be replaced. Those springs get weak and don't hold the belt as tight as they should.

 

I was going to suggest the dressing and soap but seen you already did those. No other help I can suggest than the tensioner also.

 

what type of belt are you using?

 

Most Napa belts are Gates. Very good belt. Napa branded Gates belts have 25 beginning as their part number.

The problem your brother is facing is a typical glazing of the pulleys. Once a belt gets wet and starts to squeal(means the belt is slipping) it's "polishing" the pulleys as it squeels. So, when you throw a new belt on, it's tacky enough to grab the pulleys until it gets wet again. A belt will absorb moisture and does take time to "dry" out, so with the 2 combined is why the squeel persists.
You need to take scotchbrite and scuff the pulley surfaces up that the belt rides on. This will improve bite and eliminate your sqeal.

 

I should have mentioned the top tensioner pulley has been replaced. I will have him try the scotchbrite idea to scuff the pulleys a bit. anyone else have this problem?

 

There is only one tensioner pulley. Sounds like you replaced the idler. The tensioner is below the idler.

 

He should install a new belt after doing so. Using scotchbrite on the pullies and installing the old belt to allow it to squeel will rnder the work useless and will "polish" the pulleys again. Once the belt has squealed, it itself has been polished as well and is much more prone to slipping.