hello, Scotty.
i have a 2008 Expedition with the 3 valve 5.4L V8, 98k miles. there's a squeal from the serentine belt/pulley system every time the engine is under load. it's been doing this for about 20 k miles. i first noticed it when pulling a heavy trailer, but now i hear it on every trip. it's quiet at idle, and under light loads. i first tried replacing the idler pulley, no difference, then i bought a kit at Autozone that has every pulley and a new belt. still no difference. the heavier the load on the engine, the more noise it makes. it seems to run just fine. any idea what could be causing this?
Check each accessory, could be one of those. Ford power steering loves to do that so be sure to check the level of your fluid along with the condition
Are you sure it's not your transmission instead of the belt? If low on fluid or getting ready to fail they will screech just like a belt.
I'm not sure how i'd check each accessory, as it happens when i'm driving, not in the driveway. i am certain that it's not the trans. all fluid levels are fine.
Take the fan belt off and spin each pulley by hand, feeling for roughness, noise, or looseness in the bearings.
There's also the broomhandle or stethoscope if you're comfortable next to the engine while running (if not you'll get over it fast).
Get it up to the rpm range it starts squealing by hand manipulating the throttle, then put the a cut down broomhandle or mechanics stethoscope against each component & listen for your culprit.