Chevrolet DB90 Series, Руководство по обслуживанию

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Sec. 6C-77
53 AND 71 SERIES DIESEL ENGINES
(no-load) with the sp ecifica tio n s in the "Exhaust
B ack P r e ssu re" chart.
E x c e ssiv e exhaust p r e ssu r e indicates a r e ­
str ic te d exhaust sy ste m . Inspect for:
1. L oose or broken m uffler b a ffles.
2. Sharp bends in exhaust pipe due to damage
or sp ecia l in sta lla tio n s.
3. R estricted due to carbon deposits or foreign
m atter.
4. Improper type of m uffler.
5. Exhaust pipe too long o r sm a ll in diam eter.
PROPER USE OF MANOMETER
The U -tube m anom eter is a prim ary m ea su r­
ing device indicating p r e ssu r e or vacuum by the
difference in the height of two colum ns of fluid.
Connect the m anom eter to the so u rce of p r e s ­
su r e , vacuum, or differential p r e s s u r e . When the
p r e ssu r e is im posed, add the number of inches one
colum n of fluid tr a v e ls up to the amount the other
colum n tra v els down to obtain the p r e s s u r e (or
vacuum) reading.
The height of a colum n of m ercury is read
differently than that of a colum n of w ater. M ercury
does not wet the in sid e surface; th erefore, the top
of the column has a convex m en iscu s (shape). Water
w ets the su rfa ce and th erefore has a concave men­
is c u s . A m ercury colum n is read by sighting hor­
izontally between the top of the convex m ercury
su rfa ce (fig. 21) and the s c a le . A w ater m anom eter
i s read by sighting horizontally betw een the bottom
of the concave w ater su rfa ce and the s c a le .
Should one colum n of fluid travel further than
the other colum n, due to m inor variations in the
in sid e diam eter of the tube or to the p r e ssu r e im ­
p o sed , the accuracy of the reading obtained i s not
im paired.
The m anom eter reading may be converted into
other units of m easurem ent by u se of the p r e ssu r e
con version chart.
PRESSURE CONVERSION CHART
1 ' water
s
.0735" m ercury
1 ' w ater
■
.0361 p si
1 ' m ercury
m
.491 psi
1" m ercury m 13.6" water
1 p si
m
27.7" water
1 p si
u
2.036" m ercury
OIL, FUEL, AND COOLANT LEAK
TROUBLESHOOTING
A "Troubleshooting" procedure to be u sed to
d isgn ose lea k s within the engine, fu el, or cooling
sy s te m is a s follow s:
HEIGHT
V
J
COLUMN
Hg
h
2
o
TOP SURFACE OF FLUIDS
CONVEX FOR MERCURY CONCAVE FOR WATER
Figure 21 —Com parison o f Column H eight
for
Mercury
a n d W ater M anom eter
The fir s t and m ost im portant factor is to d e­
term in e the type of dilution that e x is ts , using your
s e n se of sigh t, fe e l, and s m e ll. You m ust determ ine
if it is engine oil and w ater, fluid and w ater, or
fu el o il and engine o il. The four m ost common
typ es of dilution are:
1. W ater in engine o il.
2. Engine o il in w ater sy ste m .
3. Fuel o il in engine o il.
4. C onverter fluid in w ater.
1. Water in Engine O il
a. Injector Tube L eak s. The tubes may have
becom e cracked b ecau se of distortion by heat, o v e r -
torquing upon in jector in stallation , or im proper
sea lin g of the in jector tube sealin g ring. T his may
be checked a s follow s:
(1) Obtain norm al operating tem perature and
rem ove valve c o v e r s.
(2) P r e s s u r iz e w ater sy ste m with a te s te r as
d escrib ed in ENGINE COOLING SYSTEM
(SEC. 6K) of th is supplem ent.
NOTE: E x c e ssiv e p r e ssu r e may damage
sy ste m com ponents.
(3) O bserve a ll tubes carefully for p o ssib le
lea k s.
b. Engine Oil C ooler may put w ater in the en­
gine o il after the engine has stopped. The p r e ssu r e
m aintained in the w ater sy ste m may fo rce w ater
in o il co o ler that has a d efective co re or gasket.
To check the co o ler m ust be rem oved from engine.
E xam ine gask ets upon rem oval for sig n s of le a k s.
Make a su itab le plate and attach to the flange sid e
of the co o ler c o re. P late should be d rilled and tap­
ped to perm it a ir hose fitting to be attached to inlet
sid e of c o o ler. Attach hose and apply 75 p s i of a ir
p r e s s u r e . Subm erge co o ler co re and plate into
w ater and any leak s w ill be indicated by bubbles in
the w ater. If lea k s a re indicated, rep la ce the c o re.
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL SUPPLEMENT
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