Replace belt tensioner or just the pulley?

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I've been on a bit of a hiatus from BITOG for the last several months but hopefully back for a while now!

Our Mazda3 (~85k miles) has been making a chirping noise from its serpentine belt tensioner periodically. The belt is due for replacement anyway so the timing is convenient! I'm debating whether to replace just the pulley, or the whole tensioner though. The tensioner has a little arrow and three lines molded onto it which presumably can be used to determine whether it's working correctly (photo below). The arrow pointing at the lowest line, as it is, I would think indicates that the tensioner is weaker than it needs to be, or that the belt is a bit short (but it's the original belt). But it is technically within the lines. It holds steady while the engine is running -- no visible vibration as I've seen on failing spring tensioners in the past. The service manual lists the arrow being outside the indicators as a check on whether the belt needs replacing (and actually shows a picture of the indicator on the high side rather than the low side) but does not mention this as a check on the tensioner itself.

Would you replace this tensioner or just the pulley?

IMG_20170206_074059243_zpsblckisjl.jpg
 
I would replace the whole tensioner assembly. My top tensioner started to fail at 68K miles on a 2009 Mazda3 so this issue seems to be a known commodity and relatively common. There was no vibration of any note on mine but there was an audible sound that you didn't need a stethoscope for...however, techs confirmed that's what it was w/ a stethoscope. If you have designs on keeping the car for awhile I'd probably spring for the whole job.
 
Thanks, good info. I went ahead and ordered the whole tensioner. Will be interesting to see whether the old one still moves smoothly when it comes off.
 
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