Recommended engine oil for the GM built, diesel engines used in Hummer vehicles, is API classification CF-4 (Figure 2-3).
Base stock or synthetic oils are equally acceptable.
Oil viscosity recommendations are:
– Use 15W-40 at ambient temperatures from 0¡F (-188¡C) to above 100¡F (401¡C).
– Use 30W at ambient temperatures above 32¡F (0¡C).
– Use 10W-30 at ambient temperatures below 60¡F (165¡C).
Do not use 10W-40, or any other oil that is not specifically recommended. Use recommended oils only for lubrication purposes during repair and overhaul.
AM General suggests using Quaker State FCI-Universal HDX Engine Oil 15W-40 grade or equivalent.
