[tickerguy]

Yeah just buy the OE ones. There is a wear indicator on the tensioner; the new belt should start with the hex pointing between the two closer-together lines; when you get to where its near or at the farthest one the belt should be replaced. I typically do BOTH at 100k intervals -- the stretchy (water pump) one cannot be gotten to without removing the other, and if you break that one you're stopping right NOW.

On some cars changing them on the side of the road is not a big deal. This one would be NOT fun since the only reasonable access is through the pax side wheel well; remove the wheel and splash shield and its easy. Attempting to do it without that, well, it might be possible to get the serpentine one but it does not looks like fun.

 

[tickerguy]

Ah -- second generation. Sorry about that; the G3 cars have two.

That is a more-conventional setup (one belt) but it doesn't look like fun to get to when on the road, so the same "do it before it breaks" applies. My "general rule of thumb" on serpentine belts is 10 years or 100,000 miles. You can remove it and look at it; any cracking in the ribs on the back (say much less any other sort of deterioration) indicates that it should be replaced. It is very, very difficult to know in many cases if it is serviceable with the belt on the pulleys. I like the G3 tensioner "stretch" indicator; you need an inspection mirror to see it but it's a 30 second check when you change your oil.

A friend of mine had a car with some very minor visible cracking on the back which I could see with it on. I recommended he change it as he never had himself although he bought the car used (2005 vehicle) and when we got it off to inspect it the belt was literally coming apart with a longitudinal split of about 6" in one area!

 

[tickerguy]

If there is a shock on it and is leaking (oil on and around it) replace it. On some vehicles with a shock the shock itself can be replaced alone if the rest of the tensioner is ok.

After removing the belt check the pulley for play (bearing), along with ALL other pulleys (accessories and idlers.) Any that are in any way loose or have any sort of "grittiness" in them you can feel when rotating them by hand should be replaced.

On a serpentine belt I do not replace a tensioner (or the idler(s), if present) unless I have a reason to do so. Most of the time if/when they fail they give a decent amount of warning via odd noises first.