2008 GMC Envoy Owner's Manual - Page 342

What to Use To determine what kind of lubricant to use, see Recommended Fluids and Lubricants on page 6-12. How to Check Lubricant Front Axle When to Check Lubricant It is not necessary to regularly check front axle fluid unless you suspect there is a leak or you hear an unusual noise. A fluid loss could indicate a problem. Have it inspected and repaired. To get an accurate reading, the vehicle should be on a level surface. If the level is below the bottom of the filler plug hole, located on the front axle, you may need to add some lubricant. When the differential is cold, add enough lubricant to raise the level to 0.50 inch (12 mm) below the filler plug hole. When the differential is at operating temperature (warm), add enough lubricant to raise the level to the bottom of the filler plug hole. 5-48