Pontiac 1997 Bonneville Owner's Manual page 279

NOTICE:
If you
use an improper coolant mix, your engine
could overheat and be badly damaged. The
repair cost wouldn't
be
covered
by your
warranty,
Too
much water
in
the mix 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 t'o
add extra inhibitors or additives which claim to
improve the system. These can be harmful,
Checking Coolant
When your engine is cold, the coolant level should be at
FULL COLD or a little higher. When your engine is
warm, the level should be up to FULL HOT or
a
little higher.