If you've been following my nightmare of the belt / alternator disaster and associated problems and injuries over the past 6 weeks, then you know that I have lost my battle with the belt tensioner - and have, as a result - a load of problems.

But as part of this whole ordeal, I have found myself wondering why my car has both an idler pulley and a belt tensioner. It is a 2001 Cavalier 2.2 5-speed manual. And this model being one of the Cavalier that HAS the tensioner, contributed to my problems since from everything I've been able to find out about it - things sure were easier when you only had the idler pulley to use for getting the belt off. Anyway, I was wondering why this model - or any model of any car - has both. What purpose does my idler pulley serve if the belt tensioner does what its name says it does?
Are they redundant? Does one serve as a backup if the other fails? I'm confused. (and still sore)

Thankx

Hi.

Typically an idler pulley simply assures that the grooved portion of your serpentine belt is the side contacting each of your pulleys. Also it makes sure enough of your belt is in contact with each pulley to properly maintain friction and not be prone to slipping.

Hope that explains it.
-OBi