Chevrolet 1998 C/K Full-Size Pickup Owner's Manual page 320

NOTICE:
If you use an improper coolant mixture, your
engine could overheat and be badly damaged.
The repair cost wouldn't be covered by your
warranty. Too much water in the mixture can
freeze and crack the engine, radiator, heater core
and other parts.
If you have to add coolant more than four times a year,
have your dealer check your cooling system.
NOTICE:
If you use the proper coolant, you don't have to
add extra inhibitors or additives which claim to
improve the system. These can be harmful.
Checking Coolant
If your vehicle has a diesel engine, see "Checking
Coolant" in the Diesel Engine Supplement.
The coolant recovery tank is located on the passenger's
side at the rear corner of the engine compartment.
When your engine is cold, the coolant level should be at
the COLD mark, or a little higher. When your engine is
warm, the level should be up to the HOT mark, or a
little higher.
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