2011 GMC Savana 3500 Cargo Owner's Manual - Page 301

Vehicle Care How to Check Lubricant To get an accurate reading, the vehicle should be on a level surface. When the differential is at operating temperature (warm), add enough lubricant to raise the level to the bottom of the fill plug hole. What to Use Refer to Recommended Fluids and Lubricants on page 11‑7 to determine what kind of lubricant to use. 10-35 How to Check Lubricant Rear Axle When to Check Lubricant Refer to the Maintenance Schedule to determine how often to check the lubricant. See Scheduled Maintenance on page 11‑2. To get an accurate reading, the vehicle should be on a level surface. If you have the 1500 Series, the proper level is from 15 mm (5/8 in) to 40 mm (1 5/8 in) below the bottom of the fill plug hole. The proper level for the 2500 and 3500 Series is from 0 to 6 mm (1/4 in) below the bottom of the fill plug hole. Add only enough fluid to reach the proper level. If the level is below the bottom of the fill plug hole, some lubricant may need to be added. When the differential is cold, add enough lubricant to raise the level to 10 mm (3/8 in) below the fill plug hole.