Go ahead and change the serpentine belt, tensioner and idler roller when replacing an alternator on your car or truck.
Examine idler rollers for wear patterns. If you see wear, they're not spinning freely.
You bring your car in for a new alternator and the mechanic wants to change out the serpentine belt, the tensioner and the idle roller too. Is it worth it?
Yes. Your mechanic is actually looking after your best interests. Belts, tensioners and idler rollers rarely last the life of the vehicle. The additional labor for the idler roller is minimal (about $10), and the labor for the tensioner usually runs about $50. If you plan to keep the vehicle, you'll save money in the long run by replacing these parts now.