Inspection is the best way. Look for cracks in the belt. If you find cracks I would change the belt. If you don't know how the plugs should look check out a Haynes or Chilton and make sure the gap is correct.
Art. E. Proulx wrote:
My 97 Astro has 63K miles on it and planning a long trip south next
> winter and will add another 4000 miles.
> What is the life expectancy in miles of an original serpentine belt?
> Some sources say anywhere from 120K to 150K. Sound right?
> The van has been well cared for and driven under light to moderate > conditions.
> How about spark plugs. The original platinums are still installed. > Thanks Art
>