GMC 4000 Series Service Manual page 323

Sec. 6K
Page 312
ENGINE COO LING SYSTEM
Figure 2 — Engine Units for Overheat Switch
and Temperature G a u g e (V6 Gasoline Engine)
into engine, and exhaust gases entering cooling
system . If Ethylene Glycol anti-freeze is to be
used on vehicles having a water filter, the water
filter must be serviced at regular intervals as
directed later in this section under "Water Filter."
After anti-freeze solution has been installed, entire
system should be inspected regularly for leaks.
THAWING COOLING SYSTEM
If cooling medium in system becomes frozen
solid, place vehicle in warm place until ice is
completely thawed out. UNDER
STANCES SHOULD ENGINE
COOLING SYSTEM IS FROZEN SOLID.
The inhibited year-around (permanent-type)
engine coolant, used to fill the cooling system at
the factory is a high quality solution that meets
General Motors Specification 1899-M. This fac-
tory-fill coolant solution is formulated to with­
stand two full calendar years of normal operation
without draining or adding inhibitors, and provides
freezing protection to -20°F.
It is the owner's responsibility to keep the
freeze protection at a level commensurate with
the area in which the vehicle will be operated.
Regardless of climate, system protection should
be maintained at least to 0°F., to provide adequate
corrosion protection. When adding solution due to
lo ss of coolant for any reason or in areas where
temperatures lower than -20°F ., may occur, a
sufficient amount of an ethylene glycol base coolant
that m eets GM Specification 1899-M should be used.
G M C S E R V I C E M A N U A L
serviced by flushing with plain water, then com­
pletely refilling with a fresh solution of water and
a high-quality, inhibited (permanent type) glycol
base coolant meeting GM Specification 1899-M,
and providing freezing protection at least to read
0°F. At this time, also add GM Cooling System
Inhibitor and Sealer or equivalent. In addition,
Cooling System Inhibitor and Sealer should be add­
ed every fall thereafter. GM Cooling System In­
hibitor retards the formation of rust or scale and
is compatible with aluminum components.
ants or plain water are not recommended for your
truck at any time. DO NOT use glycol ether (methoxy
propanal type) base permanent type anti-freeze
coolants in diesel engines - damage to head gaskets
will occur.
sists of an engine thermal plug electrically con­
nected with registering gauge mounted on instru­
ment panel. Refer to applicable wiring diagram in
"Wiring Diagram" booklet. System is activated
when ignition is turned on.
either in the thermostat housing or at the front
left side of cylinder head. Unit is installed in engine
water manifold on V6 gasoline engines (fig. 2) and
in engine front cover on diesel engines (fig. 3).
CIRCUIT TEST
NO CIRCUM­
2-candlepower bulb and a pair of test leads in cir­
BE RUN WHEN
cuit by clipping one lead to battery positive term ­
inal and other lead to body of engine gauge unit. If
bulb lights, unit is properly grounded. If bulb does
not light, check for presence of sealing compound
around threads of unit. Remove compound and re­
p eat test. Make sure unit is properly grounded
before proceeding with next test.
connect lead to terminal of the unit. If bulb lights,
engine unit is internally short-circuited and should
be replaced.
unit.
above conditions, check following items according
to nature of difficulty.
turned on: This may be caused by a break in the
circuit between the gauge and the ignition switch
or a short between this lead and ground.
Every two years the cooling system should be
IMPORTANT: Alcohol or methanol base cool­
WATER TEMPERATURE INDICATOR
Electric type temperature gauge system con­
In-line engines have sending unit installed
1. Disconnect wire at engine unit.
2. Connect a test light consisting of a 12-volt,
3. Remove test lead from body of unit and
4. Remove test light and reinstall wire on
5. If engine unit tests satisfactorily under the
a. If gauge does not register when ignition is