Cooling System Diagnosis; Coolant Recovery Operation; Cto Operation - Jeep 1979 CJ-5 Technical & Service Manual

COOLING SYSTEMS 1G-5
N O T E : Immediately after shutdown, the engine enters
a condition known as heat soak, when the coolant is no
longer circulating but engine temperature is still high. If
coolant temperature rises above the bailing paint,'ex-
pansion and pressure may push some cootant out of the
radiator overflow tube. If this does not happen fre-
quently, it is considered normal.
As engine temperature drops, the coolant loses heat
and contracts, forming a partial vacuum in the system.
The radiator cap vacuum valve allows atmospheric pres-
sure to enter the system to equalize the pressure.
During operation, the coolant temperature is mon-
itored by the temperature sending unit. The sending
unit electrical resistance varies as temperature changes,
causing the temperature gauge to read accordingly.
The sender responds to temperature changes, so under
high load or on hot days, the coolant will be hotter and
the gauge will indicate higher temperatures. Unless the
gauge needle is past the high end of the band or coolant
loss occurs, this is normal.
Coolant Recovery Operation
As engine temperature increases, the coolant expands.
The radiator cap pressure vent valve (normally open)
slowly transfers expanding coolant to the coolant recov-
ery bottle. Any air trapped in the system will be expelled
during this period.
If ambient temperature is high, the system continues
heating until vapor bubbles form. These vapor bubbles
pass rapidly through the radiator cap vent valve, caus-
ing it to close. Further expansion of the coolant pressur-
izes the system up to 14 psi (96.5 kPa). Above 14 psi (96.5
kPa) the relief valve in the cap allows pressurized cool-
ant to vent to the coolant recovery system.
After shutdown engine temperature drops. The cool-
ant loses heat and contracts, forming a partial vacuum
in the system. The radiator cap vacuum valve then
opens and allows atmospheric pressure to push coolant
from the recovery bottle into the system to equalize the
pressure. Air is not admitted as long as the recovery
bottle tube remains submerged.
CTO Operation
Standard Cooling CTO Switch
The standard cooling CTO switch directs manifold
vacuum to the vacuum advance during engine warmup
to improve driveability. As engine reaches operating
temperature, the CTO switches from directing manifold
vacuum to directing carburetor ported vacuum to the
vacuum advance.
Single Function CTO Switch
The single function CTO switch directs carburetor
ported vacuum to the vacuum advance during normal
engine operation. During high heat soak periods (e.g.,
prolonged idling) the CTO switch directs manifold vac-
uum to the vacuum advance. Engine idle speed is in-
creased, thereby improving engine cooling efficiencies
and reducing idle boiling tendencies.
Dual Range CTO Switch
The dual range CTO switch operates like the standard
cooling CTO switch during engine warmup. During high
heat soak periods (e.g., prolonged idling) the dual range
CTO switch directs manifold vacuum to the vacuum
advance. Engine idle speed is increased, thereby improv-
ing engine cooling efficiencies and reducing idle boiling
tendencies.
COOLING SYSTEM D1G10IS
If the cooling system requires frequent addition of
coolant in order to maintain the proper level, check all
units and connections in the cooling system for evidence
of leakage. Inspection should be made with cooling sys-
tem cold. Small leaks, which may show up as dampness
or dripping, can easily escape detection if they are rap-
idly evaporated by engine heat. Telltale stains of a gray-
ish white or rusty color, or dye stains from antifreeze,
may appear at joints in the cooling system. These stains
are almost always a sure sign of small leaks even though
there appears to be no damage.
Air may be drawn into the cooling system through
leakage at the water pump seal or through leaks in the
coolant recovery system. Combustion pressure may be
forced into the cooling system through a leak at the
cylinder head gasket even though the passage is too
small to allow water to enter the combustion chamber.