Pontiac 1955 Owner's Manual page 27

COOLING SYSTEM
COOLING SYSTEM CAPACITIES
All Models 223^ qts.
W/Underseat Heater 24l/2 qts.
W/Air Conditioning 23 qts.
W/Air Conditioning and Underseat Heater 25 qts.
THERMOSTAT AND SEALED COOLING RADIATOR CAP-
Water temperature is controlled by a thermostat in the water outlet
elbow. When the engine is cold (below operating temperature) the
thermostat is closed a large part of the time; preventing the water
from circulating through the radiator core thus shortening the
warm-up period. This also shortens the length of time required to get
heat to your hot water heater. When the engine reaches operating
temperature the thermostat opens and allows the water to pass
through the radiator as usual.
A 7 lb. per sq. in. pressure cap is used to provide better cooling and to
help overcome the difficulty of evaporation when using volatile type
anti-freeze. A noticeable hissing or singing noise resulting from the
valve in the sealed cooling cap opening and closing may be from
engine overheating.
A 151° thermostat is used on all models. Alcohol or methanol based
volatile type anti-freeze can be used with this thermostat.
Permanent (ethylene-glycol) anti-freeze is non-evaporating. For this
reason it can be used with a higher opening thermostat available
through your Pontiac dealer.
CAUTION: Extreme care must be taken when removing radiator pressure
cap while engine is hot because relieving the pressure will cause the cooling
system to boil, if volatile type anti-freeze is used, with resultant loss of
anti-freeze solution. When removing filler cap, rotate cap toward left very
slowly; if hissing of vapor is encountered, tighten cap immediately and wait
for system to cool sufficiently to allow removal of cap. After pressure in the
system has been relieved, turn cap more forcibly to left and remove. Turn
cap all the way to the right when installing. This caution should not be
taken lightly since severe injury and fire (if alcohol and other inflammable
vapors are present) are possible if the radiator cap is removed while there is
pressure in the cooling system.
NOTE: If through some oversight the water in the radiator should get
extremely low and the engine very hot, let it cool off for ten or fifteen minutes
before adding water, then add it slowly, with the engine running. Cold water
on hot surfaces might crack the cylinder head or block.
USING RUST PREVENTIVE—Nearly all the anti-freezes on the
market today contain chemicals to inhibit rust formation in the
cooling system. When the anti-freeze is removed this protection may
[24]