The oil pan plug on a 1998 Chevy S-10 is located on the
bottom of the oil pan, which is the lowest part of the engine's oil system. To be more precise, it's usually at the
lowest point of the oil pan's underside, toward the
front of the engine.
You'll need to get under the truck to see it. It's usually a fairly large bolt or plug. Be aware that it will be hot if the engine has been recently run. Use appropriate safety precautions including jack stands and gloves.
