How often does a serpintine belt need to be changed?

I replaced my serpintine belt in December of 2004. Iti fell off my van this past week, is that normal?How often does a serpintine belt need to be changed?I change mine about every 35,000 miles just to be on the safe side but if it fell off have the tensioner checked.How often does a serpintine belt need to be changed?not normal, if it fell off you should have the idler or tensioner pulley checked by a mechanic, usually a belt will show wear (cracking, or worn places)How often does a serpintine belt need to be changed?the belt should be changed every 12 months or 20 to 30,000 milesHow often does a serpintine belt need to be changed?no,

most belt are never replaced for life of vehicles...

mechanic aligned wrong------------How often does a serpintine belt need to be changed?They're usually good at 100,000 miles. Most people change them then and keep the old one for a spare. If one fell off and wasn't broken you have a bad tensioner.How often does a serpintine belt need to be changed?It is likely a bad idler, or too lose. Nope not normal. They last a lot longer than that.How often does a serpintine belt need to be changed?I would check with the manufacturer,as they would be able to give you the best answer