I believe the serpentine belt and tensioner you are referring to in the report is the timing belt.

As you mentioned, your car has two accessory belts, neither of which are considered serpentine belts. Depending on what your visual inspection consisted of, that could still be the likely culprit either needing tightening, replacement or consideration that it could be a pulley / idler, etc.

 

I’ll try tightening both sometime this weekend and see if that helps some, then narrow it down from there if it doesn’t help. Also the CarFax said the drive belt(s) and timing belt were replaced 18k miles ago, so I wonder what the report means by serpentine…

 

Personally, I don't put much stock in Carfax reports but that's me.

As mentioned though, you don't want to tighten the belts too tight as you can cause issues with the idlers or accessories like the alternator pully / bearings, compressor, etc. I'd follow the instructions above as there should be some level of play but not a lot.

I'd also look up some videos specific to your application. I can't recall on my '03 WRX exactly but on my wife's '08 Forester I recall it had a somewhat of a "less than straightforward" way of loosening the alternator to relieve tension on one of the belts. It really depends on your level of experience and comfort wrenching on cars to figure such things out on your own and I really don't want to assume. Some setups are pretty routine.

 

Considering the car doesn't have a drive belt, nor a serpentine belt, CarFax may have been out to lunch at the time of their assessment.

A belt can look fine and squeal if the belt's pulleys are loose, or the belt slips a bit, usually when cold, because it has been worn smooth so the pulley loses its grip.

You check the belt tension by how much the belt can be deflected by pressing down / lifting the belt to assess that the it's at the proper spec. If it moves more than that, tighten it up by adjusting the appropriate pulley.

Tightening too much risks damage to the belt or what it's attached to.

If the belt looks in good shape, and tension is in spec, you can pick up some belt dressing spray at any auto parts store. Spray it on the belt and it should quiet down the belt if it passes the above tests.

 

Try twisting the belts past 90 degrees. They should not twist that much

 

@camng If it helps you any, my local shop lists accessory belts as serpentine belts on his repair invoices. Tomato.

 

They are not an old fashioned V-belt. They are multi-groove belts. Does that make them "serpentine"? I think that name is reserved for longer belts that "snake" their way back and forth around various pulleys. (Like a serpent/snake?)
Whether you call them a drive belt or not??? They drive accessories? (but they have nothing to do with "moving the vehicle", in that sense of "drive")

If there are no "chunks" missing from the belt, and they still "look" okay, they are likely just loose. (and need tightening).

You're welcome to post some photos if you want...

 

They are not an old fashioned V-belt. They are multi-groove belts. Does that make them "serpentine"? I think that name is reserved for longer belts that "snake" their way back and forth around various pulleys. (Like a serpent/snake?)

Not the former, but the latter.

 

@camng if the belt has been squealing for awhile, it may be glazed now & could need replacement?

As to tightening the belt, I always go with only what's needed, as more will stress the bearings.

Bobby...

Just in case you need this...

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