Fuel Specific Gravity Test: Description
WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The fuel quality hydrometer provides a general indication of fuel quality and should not be considered scientifically accurate. API gravity for No. 1 diesel should be 39-44 and API gravity for No. 2 diesel should be 30-39.