Chevrolet 1994 Astro Passenger Owner's Manual page 230

You should also use the proper viscosity oil for your vehicle, as shown in
the following chart:
RECOMMENDED SAE VISCOSITY GRADE ENGINE OILS
FOR BEST FUEL ECONOMY AND COLD STARTING, SELECT THE LOWEST
SAL VISCOSITY GRADE OIL
FOR
THE EXPECTED TEMPERATURE RANGE.
HOT
WEATHER
F
+
100
+
80
+
60
+
40
+
20
0
+
38
+
27
+
16
+ 4
- 7
-
18
COLD
WEATHER
LOOK FOR
ONE OF THESE
LABELS
SAE 1OW-30
SAE 5W-30
PREFERRED
IF NEITHER SAE 5W-30 NOR SAE 1OW-30
GRADE OILS ARE AVAILABLE, SAE 30
GRADE MAY BE USED AT TEMPERATURES
ABOVE 4 0 DEGREES F (4 DEGREES C).
ANY OTHER GRADE OIL NOT RECOMMENDED
DO NOT USE SAE 1OW-40, SAE 2OW-50 OR
As shown in the chart, SAE 5W-30 is best for your vehicle. However, you
can use SAE 1OW-30 if it's going to be 0°F (-18°C) or above. These
numbers on an oil container show its viscosity, or thickness. Do not use
other viscosity oils, such as SAE lOW-40 or SAE 20W-50.
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