GMC T Series 1994 Repair Manual page 542

Measure
• G low plug resistance. C onnect an ohm m eter
between the electrical connector blade and the
glow plug body. Replace any glow plug with a
resistance greater than 2 ohms.
THERMOSTAT AND COOLANT
CROSSOVER
There are two different types of thermostats used on
the 6.5L diesel engine. The C/K models use a " blocking
bypass" type thermostat. The poppet at the bottom of
this thermostat closes off the coolant bypass hose when
the engine is at operating temperature and the thermo­
stat is fully open. This causes all coolant to flow
through the radiator. Due to space restrictions, the P
truck and G-van models use a conventional " balance
type" thermostat. Refer to SECTION 6B1 in the appro­
priate application service manual.
Disassemble (Figure 19)
*
1. Bolts or studs (106).
2. Coolant outlet (107).
3. Thermostat (108).
4. Gasket (103).
L*
Inspect
• Coolant outlet and coolant crossover for cracks.
Thermostat Check
1. Suspend the thermostat and a thermometer in
water with the thermometer located close to the
thermostat. The thermostat must be completely
submerged and the coolant thoroughly agitated
while heating. Apply heat to the coolant and record
both the tem perature at which the therm ostat
begins to open and the temperature at which the
thermostat is fully open. The thermostat should
begin to open at 1.6°C (4°F) above or below the
temperature stamped on the thermostat. It should
be fully open at approximately 13°C (24°F) above
the stamped temperature located on the thermo­
stat.
2. Do not attempt to repair the thermostat. If the
thermostat does not function properly, replace it
with a new unit which has been checked as direct­
ed previously.
Install or Connect (Figure 19)
1. Gasket (103).
2. Thermostat (108).
3. Coolant outlet (107).
N O T IC E : R e f e r to "N o t i c e " o n p a g e 6 A 7 -1 .
4. Bolts or studs (106).
Tighten
IN JEC TIO N NOZZLE TESTS
Tool Required:
J 29075-B Nozzle Tester
J 29079-125 Adapter Kit
J 29079-1 Line Assembly
J 29079-3 Adaptor Nut
J 29079-18 Adaptor
J 29079-13 Manifold Adaptor
J 7660-101 Washer
Nozzle testing is comprised of the following checks:
• Nozzle opening pressure
• Leakage
• Chatter
• Spray pattern
Each test should be considered independent of the
others. For example, when checking opening pressure,
do not check for leakage.
If all of the above checks are okay, the nozzle holder
assembly can be reused. If any one of the checks is
not okay, the complete nozzle holder assembly must be
replaced. The nozzle holder will then be checked and
repaired at a centralized location.
When performing the injection nozzle tests,
the in s tru c tio n s provided w ith the nozzle te ste r
J 29075-B.
•Test Lines - 6x2x400-mm (1.5-mm bore).
•Test Fiuid - per ISO 4113 (Example: Shell V 1399,
Viscosity 1487C or equivalent).
• Kinetic Viscosity at 4°C (40°F) - per ISO 3104: 2.45
to 2.75 mm/second.
• Test oil temperature during test: 20 to 25° C (68° to
77°F).
1. Connect the nozzle holder assembly to the test
line.
2. Place clear plastic tubes on overflow connections
to prevent leakoff from being confused with actual
leak.
3. Close the shutoff valve to the pressure gage.
CAUTION: When testing nozzles, do not place
your hands or arms near the tip of the nozzle.
The high pressure atomized fuel spray from a
nozzle has sufficient penetrating power to
puncture flesh and destroy tissue and may
result in blood poisoning. The nozzle tip
should always be enclosed in a receptacle,
preferably transparent, to contain the spray.
4. Fill and flush the nozzle holder assembly with test
oil by activating the lever briskly and repeatedly.
This will apply test oil to all functionally important
areas of the nozzle and purge it of air.
OPENING PRESSURE TEST
I.O p e n the shutoff valve at the pressure gage
one-quarter turn.
CAUTION: When testing nozzles, do not place
your hands or arms near the top of the noz­
zle. The high pressure atomized fuel spray
from a nozzle has sufficient penetrating pow­
er to puncture flesh and destroy tissue and
may result in blood poisoning. The nozzle tip
should always be enclosed in a receptacle
preferably transparent, to contain the spray.
to
refer