When my truck is running its making a high
pitched squeal replaced serpintine belt but
still making noise
Check the idler pulleys, may be worn, if the new belt is squealing, either the belt tensioner needs replacing, or there is a foreign substance that needs to be cleaned off the pulleys.
How do u tell if its worn out or nothing
There are marks on the tensioner that should be close together when the belt is on. This indicates wear in the belt. It may be you might have to get the next shorter belt if those marks are not close. If they are then I would replace the belt tensioner.
Check all the pulleys on the engine for binding. Check the pulley for the AC first, this one usually goes out when the clutch goes bad.
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