Chevrolet 70 Series 1970, Service Manual

Page: 832 / 841

RADIATOR AND SURGE TANK 13-6
Cap Unit
Vacuum
Valve
Pressure Valve
Pressure
Valve
Spring
Figure 7 —Combination Pressure Relief Valve and Filler Cap
radiator to the fram e sid e r a ils , the radiator sid e
adjustm ent can be made a s follow s:
L oosen both adjusting bolt lock nuts (14, fig . 4)
at each sid e of radiator trunnion mounting b rack ets.
B ack bolt out of mount in the direction of the de­
s ir e d m ovem ent. Thread bolt inward on opposite
sid e of radiator until radiator is centered a s de­
s ir e d . Make certain that both adjusting b olts are
tight against radiator trunnion, and that no sla ck
e x is ts . Tighten adjusting bolt lock nuts firm ly .
RADIATOR SURGE TANK
vapor is allow ed to esca p e. A s liquid in sy ste m
co o ls it contracts; th is allow s p r e s s u r e valve to
c lo s e and a lso cre a te s a p a rtia l vacuum in sy ste m .
A tm ospheric p r e ssu r e acting through overflow
tube u n seats vacuum valve and allow s air to enter
sy ste m . The overflow pipe connects to valve out­
sid e the valve seal; thus no liquid o r air can e s ­
cape from the sy ste m when both v a lv es are in the
c lo se d position .
R adiator fille r cap is constructed with a sp rin g-
loaded rubber s e a l which is p r e s s e d firm ly against
su r fa ce of fille r neck se a t when cap is in stalled .
Rubber s e a l m ust be in good condition and top of
radiator fille r neck must be clean and sm ooth in
ord er to form an a ir-tig h t s e a l. Seal of f ille r cap
and operation of p r e ssu r e r e lie f valve can be
checked using a conventional cooling sy ste m te s t ­
ing kit.
NOTE: When engine is at norm al operating
tem perature or above, the internal p r e ssu r e built
up in the cooling sy ste m w ill blow out scalding
fluid and vapors if the radiator cap is suddenly
rem oved. To prevent lo s s of coolant and to avoid
the danger of being burned, the coolant le v e l should
be checked or coolant added only when the engine
i s co o l. If the cap m ust be rem oved when engine is
hot, p la ce a cloth o v er the cap and rotate the cap
slow ly counterclockw ise to fir s t stop and allow
p r e ssu r e to esca p e com pletely. Then turn cap
again slow ly counterclockw ise to rem ove.
NOTE: A sp e c ia l testin g kit for radiator fille r
caps can be obtained lo c a lly . Instructions supplied
with kit should be follow ed.
A sep arate radiator surge tank is used on
so m e m odels covered by th is manual. The su rge
tank s e r v e s as a coolant r e se r v o ir for the radiator
c o r e which is mounted low to front of engine. H oses
and p ipes connect tank to radiator and w ater pump.
Supply tank incorporates the cooling sy ste m fille r
cap which is a c c e ssib le on s te e l tilt cabs from in­
sid e cab through sm a ll door at top of sea t r is e r .
To gain a c c e s s to supply tank its e lf, tilt cab fo r ­
ward.
At regular in tervals connecting h o ses betw een
su rg e tank and radiator should be checked for
le a k s . Keep a ll h ose clam ps and mounting b olts
tightened se c u r e ly .
PRESSURE RELIEF VALVE
AND FILLER CAP
P r e s s u r e r e lie f valve assem b ly , integral with
radiator fille r cap, incorporates a p r e ssu r e valve
and a vacuum v a lv e (fig. 7). When p r e ssu r e in
s y s te m rea ch es valve settin g (se e "Specifications"
at end of th is sectio n ), p r e ssu r e valve opens and
ENGINE COOLANT
COOLANT RECOMMENDATIONS
The year-around engine coolant used to fill
the cooling sy ste m at the factory is a high quality
solution that m eets G eneral M otors Specification
1899-M . This fa c to r y -fill coolant solution is form ­
ulated to withstand two full calendar y e a r s of norm ­
al operation without draining or adding inhibitors,
provided the sam e concentration of coolant is add­
ed if the sy ste m needs additional fluid between
drain p erio d s. The original factory fill coolant
p rovid es freezin g protection to -2 0 ° F .
E very two y e a r s, the cooling sy ste m shouldbe
se r v ic e d as d escrib ed in ENGINE COOLING SYS­
TEM (SEC.
6
K) of th is manual. A thorough d es­
cription of inspection, draining, and cleaning of the
cooling sy ste m is given.
IMPORTANT: A lcohol, methanol base cool­
ants, or plain water a re not recom m ended. Only a
su fficien t amount of Ethylene G lycol b ase coolant
m eeting GM Specification 1899-M should be used .
DO NOT u se glycol ether (methoxy propanal type)
b ase perm anent type a n ti-fr e e z e coolants in DH
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL