It is probably not a belt, but rather a chain
It has a timing chain which will last the life of the engine.
Timing CHAIN on the 2.5 liter V6 in a 1999 Suzuki Grand Vitara
Your 1999 Chevy blazer doesn't have a timing belt.
A computer diagnostic test will show a timing belt problem for a 1999 Mazda 626. If there is a problem with the belt, diagnostics will determine if it needs to be repaired or replaced.
The timing belt needs to be replaced about every 100k miles. Actually the recommended interval is 105,000 miles. You also replace the tensioner and idler pulley at this time
a timing chain
You would need to pull one of the covers off and look at its physical condition.
This is like asking "when should I have the cylinders reground or the oil pump replaced. A timing chain is not like a timing belt in that it is not subject to 80,000 mile replacement. So, keep your oil changed every 3000 miles and drive on.Good luck !!!
about 100,000 mile if it,s a timing belt
It does not have a timing belt. It has a timing chain.It does not have a timing belt. It has a timing chain.