its a dynasty 3.3. why doesn't the serpentine belt stay on on 1990 Dodge D250

this last summer i bought my granddaughter a 1990 dodge dynasty. we've put on three serpentine belts on and they keep coming off. can someone help me? from lorraine.
crying in drayton nd

Asked by for the 1990 Dodge D250
1 answer 1 comment
TRY A NEW BELT TENSIONER
i'm sorry, i guess i forgot to say we did that also. but thanks for a good answer.lorraine