1998 Ford Explorer

Hi Rene, Does it continue to squeal or does it stop after warm up? There are a couple possibilities.... The belt is worn and slipping The tensioner is weak causing the belt to be loose and slipping The Bearings in the tensioner pulley are going bad. or the Bearings in the Idler pulley are going bad. Here is a quick test for checking pulley bearings... With engine off locate tensioner pulley and Idler pulley. With some spray lube in hand spray the center bolt of one of them NOT Both. Start vehicle if squeal is gone for short time replace that pulley. If noise still there turn engine off and spray center bolt of other pulley and start engine again. If noise is gone for short time replace that pulley. If squeal is still there watch the tensioner assembly if it seems to move pretty freely mean it bounces a lot. Then could be then tensioner assembly . If tensioner seems pretty steady and doesn't move a lot the spray the belt itself is squeal stops replace belt. Below are two diagrams depending on if the engine is OHC or not OHC

NON OHC

.