GMC 2007 Sierra - Manual (Page 530)

How to Check Lubricant
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 to 3/8 inch
(9.5 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.
What to Use
To determine what kind of lubricant to use see
Recommended Fluids and Lubricants on page 629.
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