Chevrolet 70 Series 1970, Service Manual

Page: 471 / 841

ENGINE COOLING SYSTEM 6K-4
to flow through the ra d ia to r, w here it is again
cooled to m aintain p ro p e r operating te m p e ra tu re .
INSPECTION OF SYSTEM
Although action of the cooling sy stem controls
the operating te m p e ra tu re of the engine, im p ro p er
ignition tim ing (gasoline engines) o r im p ro p er o r
insufficient lubricatin g oil in the engine cran k ca se
may cause the engine to o verheat, even though the
cooling sy stem is functioning p ro p e rly . T hese
ite m s should also be checked fo r cause of im p ro p er
cooling.
Cooling s y ste m s m ust be kept a ir-tig h t. As the
p r e s s u r e in the sy ste m r a is e s the boiling point of
the coolant, any a i r leak would low er boiling point
and re s u lt in lo ss of coolant. Check ra d ia to r cap
se a l and a ll ra d ia to r connections. E n tire cooling
sy stem can be checked fo r leaks in ca stin g s, con­
nection ho ses, g ask e ts, p r e s s u r e valves, and fille r
cap using a conventional cooling sy stem testin g kit
which can usually be obtained locally.
CAUTION: When the engine is at
normal operating temperature or above,
the internal pressure built up in the cool­
ing system will blow out scalding fluid
and vapors if the radiator cap is suddenly
removed. To prevent loss of coolant and
to avoid the danger of being burned, the
coolant level should be checked, or cool­
ant 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 ro­
tate the cap slowly counterclockwise to
firs t stop and allow pressure to escape
completely. Then turn cap again slowly
counterclockwise to remove.
DRAINING COOLIN G SYSTEM
1. Remove ra d ia to r fille r cap.
2. Rem ove plug o r open d ra in cock at bottom
of ra d ia to r co re.
3. Open petcock o r rem ove d rain plug at each
sid e of cylinder block.
a. On m odels with 6-71N engines, open d ra in
cocks a t bottom of th erm o stat housing (if equipped),
w a te r pum p, oil cooler, and cylinder block at r e a r
of blow er below fuel pump (fig. 5).
b. On a ll 8V engine m odels, open d rain cock at
each side of engine cylinder block (Low er Views,
fig. 6). At rig ht sid e of engine, open d rain cock at
bottom of engine oil cooler (Upper Right View,
fig. 6).
4. If tilt cab model, p lace h e a te r te m p e ra tu re
con tro l in "HEAT" position.
5. Rem ove d ra in plug fro m bottom of engine
o il co oler (if equipped).
W A TE R M A N IFO LD
TO SURGE T A N K
Figure 3—Coolant C irculation 16-71 Diesel EngineI
6. Remove d rain plug from bottom of cooling
sy stem filte r assem bly (if equipped).
7. If vehicle is equipped with a w a te r-c o o le d
a i r c o m p re sso r, disconnect a i r co m p re sso r cool­
ant hose from sid e of cylinder block.
FILLING CO O LIN G SYSTEM
When cold w ater is poured into the ra d ia to r,
the th e rm o sta ts w ill clo se even though the engine
is w arm . T his action may trap a i r in cylinder
block and head p a ssa g e s. The trapped a ir w ill leak
through the th e rm o sta t vents thereby low ering the
w a te r level.
Use The Following Method When F illin g System:
1. If vehicle is equipped with h e a te r, the con­
tr o l valve (tilt cab m odels) m ust be wide open be­
fo re filling cooling sy stem . This operation is to
p re v en t a ir fro m being trap p ed in h e a te r and lin es.
2. When checking level of coolant, rem ove
ra d ia to r cap SLOWLY (if engine is hot). No addi­
tio nal w a te r is re q u ire d if w ater is visible in fille r
neck o r a t bottom of fille r tube.
3. F ill ra d ia to r until w ater can be seen through
fille r neck o r to bottom of fille r tube.
4. Add m ore w a te r slowly until no m ore a ir
bubbles can be seen. Run engine a few m inutes to
fu rth e r expel a ir , then add m ore liquid if n ec es­
sa ry to bring it up to p ro p e r level.
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL