1996 GMC Sonoma Owner's Manual - Page 246

How to Check Lubricant If the differential is cold, add enough lubricant to raise the level to 1/2 inch (12 mm) below the filler plug hole. What to Use Refer to the Maintenance Schedule to determine what kind of lubricant to use. See "Recommended Fluids and Lubricants" in the Index. Engine Coolant The cooling system in your vehicle is filled with new DEX-COOL (orange-colored, silicate-free) engine coolant. This coolant is designed to remain in your vehicle for 5 years or 100,000 miles (1 66 000 km), whichever occurs first. TM If the level is below the bottom of the filler plug hole, you'll need to add some lubricant. If the differential is at operating temperature (warm), add enough lubricant to raise the level to thebottom of the filler plug hole. The following explains your cooling system and how to add coolant when it is low. If you have a problem with engine overheating, see "Engine Overheating" in the Index. 6-24