Chevrolet 1998 C/K Full-Size Pickup Owner's Manual page 307

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
20W-50.
NOTICE:
Use only engine oil with the American Petroleum
Institute Certified
For
Gasoline Engines
"Starburst" symbol. Failure to use the
recommended oil can result in engine damage not
covered by your warranty.
GM Goodwrench@ oil
meets
all the requirements for
your vehicle.
If you are in an area where the temperature falls below
-20°F (-29"C), consider using either an
SAE
5W-30
synthetic oil or an
SAE
OW-30 oil. Both will provide
easier cold starting and better protection for your engine
at extremely low temperatures.
Engine Oil Additives
Don't add anything to your oil. Your dealer is ready to
advise if you think something should be added.
When to Change Engine Oil
If
any one of these is true for you, use the short tripkity
maintenance schedule:
Most trips are less than
5
to 10 miles
(8 to
16 km).
This is particularly important when outside
temperatures are below freezing.
driving in stop-and-go traffic).
off-road frequently.
0
Most trips include extensive idling (such as frequent
You operate your vehicle in dusty areas or
0
You frequently tow a trailer.
0
The vehicle is used for delivery service, police, taxi
or other commercial application.
Driving under these conditions causes engine oil to
break down sooner. If any one of these is true
for your
vehicle, then you need to change your oil and filter
every 3,000 miles ( 5 000 km) or 3 months
--
whichever
occurs first.
If none of them is true, use the long trip/highway
maintenance schedule. Change the oil and filter every
7,500 miles (12 500 km) or 12 months
--
whichever
occurs first. Driving a vehicle with a fully warmed
engine under highway conditions causes engine oil to
break down slower.
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