I'm only running this way for testing purposes, it's temporary.  I DO NOT NEED RECOMMENDATIONS or discussion about how bad of an idea this is. 

I've driven a few hundred miles and the top smooth surface of the Subaru belt is showing odd grooving and uneven wear.   It's never touched any fluids and belt and pulleys are all OEM and only 5 years old with maybe 50,000 miles.  I checked them just in case although there's really no way for a pulley to cause such uneven wear.

All of the pulleys and water pump seem fine - so I'm wondering what's causing this - could it be the heat from the exhaust coming up from those 2005+ odd exhuast systems that run forward under the timing belts?  That seems really unlikely but I've also never seen a timing belt do this before.  

I'm going to install new pulleys and water pump and timing cover, but I'd also like to know for sure what's causing this. 

Got pics to show the wear?

Something must me misaligned - an idler pulley that’s worn, the water pump shaft worn out but this usually results in a leaking water pump. 

What about the belt-tensioner? Is it behaving itself?

And another possible suspect: the belt guide-shoe, above one of the pulleys? (only installed on manuals, I think)

Edited September 26, 2025Sep 26 by forester2002s

Thanks guy. 

18 hours ago, el_freddo said:

Got pics to show the wear?

Something must me misaligned - an idler pulley that’s worn, the water pump shaft worn out but this usually results in a leaking water pump. 

 

The tensioner does look suspect - the small pin that pushes against the bracket to create tension looks somewhat mis-marked like it's not contacting evenly.  I'll go ahead and replace that. 

It's OEM - I'm about to restart it with a new belt, I'll see if I can see the tensioner flopping around at all.  I had a 1997 EJ22 tensioner (same one piece style) do that - I guess lost hydraulic pressure and was slapping a bit until it warmed up.  Though I don't recall it wearing the belt weird. 

17 hours ago, forester2002s said:

What about the belt-tensioner? Is it behaving itself?

And another possible suspect: the belt guide-shoe, above one of the pulleys? (only installed on manuals, I think)

I'll try to post a pic.  It's very odd - like a worm ate through the top of the belt in spots...I'm exaggerating the car was still driving but it seems like anything pulley related would simply be straight not curved and wiggling across the surface. 

 

Did you still have the back plastic cover on?  Guessing a pebble wedged in somewhere for a bit then got spit out.  The plastic cover can flex around while the pebble was wedged.

Manual transmission cars have the guide over the crank sprocket. I've seen the belts get grooved up if that's adjusted too tight. But I assume you've encountered that.

I've not noticed any wear like that on a 2005+ car with the covers on.