GMC 4000 Series Service Manual page 325

Sec. 6K
Page 314
ENGINE COOLING SYSTEM
H o s e to H e a te r C o re
R etu rn Lin e F ittin g
(2) M o u n tin g B o lts,
N u ts , a n d W a s h e r s
D r a in P lu g
Figure 4 — C ooling System Water Filter Installed (Typical)
NOTE: To assure proper cooling and engine
warm-up it is very important that the correct
thermostat is used. Refer to "Specifications" at
end of this section for thermostat application.
THERMOSTAT CHECK
If it is suspected that thermostat is not func­
tioning properly, remove thermostat assembly. If
the thermostat appears to be in good condition, the
following test should be conducted.
Suspend thermostat and thermometer in water
with thermometer located close to thermostat.
Thermostat must be completely submerged and
water thoroughly agitated while heating. Apply heat
to the water and record both the temperature at
which the thermostat begins to open and the temp­
erature at which the thermostat is fully open.
Compare temperature readings taken in the
test with those given under "Thermostats" in "Spec­
ifications" at end of this section.
Do not attempt to repair thermostat. If thermo­
stat does not function properly, replace with new
unit which has been checked as directed previously.
Use new gasket when installing thermostat. Fill
cooling system then run engine until normal oper­
ating temperature is reached. Check for coolant
leakage at thermostat cover gasket.
G M C S E R V I C E M A N U A L
hicles is used to filter and condition water in cool­
ing system On a new engine, the filter element
should be initially changed after 2,500 to 3,000
m iles. After initial change, the filter should be
Filte r
serviced periodically 7,500 to 10,000 miles or 300
A s s e m b ly
to 500 hours depending upon engine workload, con­
ditions, etc.
in system should be a golden yellow. No rust pre­
ventive or inhibitor should be used in system when
water filter is used„
freeze solutions may contain inhibitor which will
produce a green residue or precipitation. If this is
noted more frequent element change periods will be
necessary and if this fails to correct condition, the
filter element should be removed, or disconnected.
ELEMENT REPLACEMENT
H o se to H e a te r
C o re In le t F ittin g
off filter supply and return hose by clamping v ise-
grip pliers to each hose if if equipped with shut-
off cocks, close cocks. Otherwise drain system .
(2) to filter. Remove cover and cover gasket (3).
plate (6), and spring (7) from filter body (8). Flush
out filter body.
then clean all parts. Examine element lower plate
for excessive corrosion.
placement. Clean plate by wire brushing. This
plate generates current for the electro-chem ical
action of the filter element. If excessively cor­
roded, replace.
(7), lower plate (6), new element (5), and upper
plate (4) in filter body. Install cover (2) using new
gasket (3). Tighten cover attaching bolts evenly
and firmly.
and operate engine until water in cooling system
is warm. Check for air lock in filter. If cover of
filter becomes warm, no air-lock condition exists
in system . If cover remains cool, vent system
same as for a hot water heater system.
to cylinder block, otherwise electro-chem ical ac­
tion of filter element will be affected.
WATER FILTER
Water filter (fig. 4) as installed on some ve­
Except when anti-freeze is used, color of water
IMPORTANT: Some permanent-type anti­
NOTE: Key numbers in text refer to figure 5.
1. For convenience in changing element, close
2. Remove two bolts (1) which attach cover
3. Remove drainplug (9) from bottom of filter.
4. Remove upper plate (4), element (5), lower
5. Discard filter element and cover gasket,
NOTE: Deep pits in plate do not warrant re­
6. Referring to illustration, position spring
7. Remove vise grips from filter hoses. Start
8. Refill system to proper level.
9. Make sure that filter body is grounded back