Cadillac 1967 VVI Data Book page 181

The cooling system is designed to maintain efficient engine
operating temperatures. Check coolant level at each engine
oil change to make certain proper level is maintained. Coolant
level with engine cold, at room temperature, should be three
inches below bottom of filler neck. Coolant level with engine
hot, at normal operating temperature, should be one inch
below bottom of filler neck. Do not overfill. Proper levels
are shown on label below radiator filler cap. Eabh fall inspect
the system for leaks and for adequate freeze protection. Refer
to page 53 for the capacity of your car's cooling system.
Caution
When the engine is at normal operating temperature or above,
the internal pressure built up in the cooling system will blow
out scalding fluid and vapors if the radiator cap is removed.
To prevent loss of coolant and to avoid the danger of being
burned, the coolant level should be checked or coolant added
only when the engine is cool. If the cap must be removed when
the engine is hot, place a cloth over the cap and rotate the cap
slowly counterclockwise to first stop and allow pressure to
escape completely. Then turn cap again slowly counterclock-
wise to remove.
WARNING: Radiator cap must be tight when re-
installed. Make certain red stripe on cap lines up with red
stripe on instruction label on radiator cradle.
The temperature gage can sometimes register " H " (Hot)
under severe operating conditions. However, this is not neces-
sarily cause for alarm unless accompanied by a buzzing noise
from the radiator cap or by loss of coolant by boiling.
CAUTION: If gage indicates above-normal temperature,
make certain engine is running, or is allowed to cool down
to normal temperature, before adding coolant.