Here is oil viscosity information for 82-12. The information comes from either the Service Manual for the model year in question or, in cases where the Service Manual refers to the Owner's Manual, the information comes from the Owner's Manual.
82--10W30, 10W40, 15W40, 20W40, 20W50, 30
(for extended operation in low ambient temperature 5W20, 5W30
84--10W30, 10W40, 15W40, 20W40, 20W50, 30
(for extended operation in low ambient temperature 5W30
85--(researching)
86--(researching)
87--(researching)
88--(researching)
89--5W30 recommended, 10W30 allowed if ambient temp is above 0°F, SAE30 allowed if ambient temp is above 40°F
90--5W30 recommended, 10W30 allowed if ambient temp is above 0°F, SAE30 allowed if ambient temp is above 40°F, LT5 only 10W30 required
91--5W30 recommended, 10W30 allowed if ambient temp is above 0°F, SAE30 allowed if ambient temp is above 40°F, LT5 only 10W30 required
92--GM4718M required, 5W30 recommended, 10W30 allowed if ambient temp is above 0°F, for LT5 only 10W30 recommended
93--GM4718M required, 5W30 recommended, 10W30 allowed if ambient temp is above 0°F
94--GM4718M required, 5W30 recommended, 10W30 allowed if ambient temp is above 0°F
95--GM4718M required, 5W30 recommended, 10W30 allowed if ambient temp is above 0°F
96--GM4718M required, 5W30 recommended, 10W30 allowed if ambient temp is above 0°F
97--GM4718M required, 5W30, 10W30, other viscosities not recommended, 20W50 not allowed
98--GM4718M required, 5W30, 10W30, other viscosities not recommended, 20W50 not allowed
99--GM4718M required, 5W30, 10W30, other viscosities not recommended, 20W50 not allowed
00--GM4718M required, 5W30, 10W30, other viscosities not recommended, 20W50 not allowed
01--GM4718M required, 5W30, 10W30, other viscosities not recommended, 20W50 not allowed
02--GM4718M required, 5W30, 10W30, other viscosities not recommended, 20W50 not allowed
03--GM4718M required, 5W30, 10W30, other viscosities not recommended, 20W50 not allowed
04--GM4718M required, 5W30, 10W30, other viscosities not recommended, 20W50 not allowed
05--GM4718M required, 5W30 recommended, other viscosities not recommended, 10W40 or 20W50 not allowed
06--GM4718M required, 5W30 recommended, other viscosities not recommended, 10W40 or 20W50 not allowed
07--GM4718M required, 5W30 recommended, other viscosities not recommended, 10W40 or 20W50 not allowed
08--GM4718M required, 5W30 recommended, other viscosities not recommended, 10W40 or 20W50 not allowed
09--GM4718M required, 5W30 recommended, other viscosities not recommended, 10W40 or 20W50 not allowed
10--(researching)
11--(researching)
12--(researching)
Important to note:
In 1992, GM4718M was not required for the LT5.
From 1997 to 2004, the only requirements are: an oil which meets GM4718M and that 20W50 not be used. 5w30 is only recommended and other viscosities between 5W30 an 20W50, while not recommended, are not prohibited.
From 2005-2009, the only requirements are: an oil which meets GM4718M and that 10W40 and 20W50 not be used. 5w30 is only recommended and viscosities between 5W30 and 10W40, while not recommended, are not prohibited.
This is a work in progress. I'll post more over the next few days