Where is the engine coolant drain plug on a 1991 Chevy Silverado 5.7L engine?

The exact location of the engine coolant drain plug on a 1991 Chevy Silverado 5.7L (likely a TBI) engine can vary slightly depending on the specific configuration, but it's generally located on the lower part of the engine block, near the passenger side (right side as you're facing the engine).

It's usually a hex-head bolt or plug and often below the thermostat housing. You'll likely need to get under the truck to access it. It's a good idea to consult a repair manual specific to your year and model Silverado for a precise location and diagram. A Chilton's or Haynes manual would be helpful.

Important Note: Before draining coolant, be sure the engine is completely cool to prevent burns. Have a suitable container ready to catch the coolant. Also be aware that the coolant is likely to be toxic, so handle it appropriately.