The owners’ manual just says to check the drive belt at 150,000 miles. My 2004 Colorado only has 91,000 miles and has not been driven in extreme conditions. Since the belt is 14 years old, should it be replaced now even though it appears to be in good condition?
Yes, I would replace it based on age alone. I recently replaced the serpentine belt on my Toyota at 8 years as it was showing small cracks.
I think that age alone is not a factor, but the age is one contributor to the symptoms that warrant replacement. The information given itemizes those contributors of those symptoms, including age.
At the age and mileage on your belt, why not replace it, quit worrying about it, and go another decade or so?
Gates, A Leading Belt Manufacturer Offers Some Guidance:
https://www.gatestechzone.com/en/problem-diagnosis/accessory-drive-system/micro-v-belt-wear-symptoms
CSA
Replace the belt.
Some auto parts stores have these serpentine belt wear indicators for free.
http://www.gates.com/products/automotive/new-products/belt-wear-gauge (watch the video)
But from the mileage/time, the belt probably requires replacement.
Tester
The owners' manual just says to check the drive belt at 150,000 miles. My 2004 Colorado only has 91,000 miles and has not been driven in extreme conditions. Since the belt is 14 years old, should it be replaced now even though it appears to be in good condition?First I gotta ask, your 2004 was actually built in 2002? But even at 12 yrs/91,000 just go ahead a replace the belt, it owes you nothing. Even with the manual saying check, not replace at 150,000, the manual probably only says check the trans fluid too.