Two things to consider on the belt tensioner:
First is the bearing, if it spins freely and smooth and makes no noise, then the bearing is ok.
Second is the tension spring; they lose tension over time and especially when ran with a bad decoupler bearing on the alternator.
next:
After you install new alternator and serpentine belt, watch the tensioner pulley at idle with the AC on and the AC compressor engaged.
if the tensioner pulley is bouncing up and down, then the tensioner spring has gotten weak and the whole assembly should be replaced.
Best places to purchase are:
IDParts:>
https://www.idparts.com/liberty-crd-ser ... -2826.html (ON SALE $129.50)
(Direct from the OE manufacturer Litens, made in Germany)
or
Sasquatch Parts:>
https://shop.sasquatchparts.com/product ... -2-8l-crd/ (revised design tensioner with a stronger pulley $160.00)
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