2008 3.0 Outback.  Changed the air filter today and took a look at the serpentine belt and am at a lost how it is adjusted.  All the idlers appear to me to be nonadjustable and it doesn't appear anyway the alternator can be moved to tighten the belt. 

try this http://www.justanswer.com/uploads/HammerTime/2006-10-01_185823_Subaru_3.0_outback_tensioner_pic.gif

Got it. Thanks. 

Hey John! Auto tensioner.

 

If it's making noise, Check the bearings soon.

 

The serpentine belt pulley bearings (idler and tensioner) in those H6 engines fail all the time and can at very low mileages. I consider them 60k replacement items or on anything a few years old with unknown history.

 

They're super easy to replace. Standard 6203 bearings and just tap them out of the pulley and tap new ones in. You'll find it a breeze.

 

Just make sure you don't loose the captive nut that the bolt threads into when removing/installing the bolts.

Edited May 20, 20178 yr by grossgary

Did a little research and decided to just buy the complete kit.  All save the original parts, replace the bearings someday and have them around to use in the future. I keep cars a long time. Still driving the 95 with around 300k miles on it. One question:  Is the bolt that retains the tensioner reverse threaded?  What nipper posted appears to loosen, turn CW.