Buick 2004 Rainier Owner's Manual page 340

How to Check Lubricant
5-52
To get an accurate reading, the vehicle should be on
a level surface.
The proper level is from 0 to 3/8 inch (0 to 10 mm)
below 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 6-12.