1997 GMC Sonoma Owner's Manual - Page 262

Front Axle When to Check and Change Lubricant Refer to the Maintenance Schedule to determine how often to check the lubricant and when to change it. See "Scheduled Maintenance Services" in the Index. If the differential is at operating temperature (warm), add enough lubricant to raise thelevel to the bottom of the filler plug hole. 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 How to Check Lubricant Refer to theMaintenance 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 DEX-COOL' engine coolant.This coolant is designed to remain in your vehicle for 5 years or 150,000 miles (240 000 km), whichever occurs first, if you add only DEX-COOL@ extended life coolant. The following explains your cooling system and how to add coolant when it is low. If you havea problem with engine overheating, see"Engine Overheating" in the Index. If the level is below the bottom of the filler plug hole, you'll need to addsome lubricant.