Page 1657 of 3573
ENGINE COOLING 6B Ð 3
The cooling system is a pressurized coolant forced
circulation type which consists of water pump, thermostat
cooling fan, radiator and other components. The
circulating coolant cools the lubricating oil in the oil filter
and turbocharger.
WATER PUMP
The coolant pump is a centrifugal impeller type and is
driven by V type drive belt.
THERMOSTAT
The thermostat is a wax pellet type with a jiggle valve and
is installed in the thermostat housing.
RADIATOR
The radiator is a tube type with corrugated fins. In order
to raise the boiling point of coolant, the radiator is fitted
with a cap in which the valve is operated under the
pressure.
Page 1658 of 3573

6B Ð 4 ENGINE COOLING
ANTI-FREEZE SOLUTION
·Relation between Mixing ratio and Freezing point
Freezing temperature of the engine coolant varies
with the ratio of anti-freeze solution in water.
Proper mixing ratio can be determined by refering to
the chart. Supplemental inhibitors or additives
claiming to increase cooling capability that have not
been specifically approved by Isuzu are not
recommended for addition to the cooling system.
·Calculation of mixing ratio
Mixing ratio
Note: Anti-freeze solution + Water = 8.6 lit
Total cooling system capacity.
=Anti-freeze solution (Lit/qt.)
Anti-freeze solution (Lit/
qt.) + Water (Lit/qt.)
In case of 6.8 lit total cooling system capacity
Mixing
ratio (%)Anti-freeze
solution:
lit. (imp. qt./U.S. qt)Water:
lit. (imp.qt/U.S. qt)
0
5
10
15
20
25
30
35
40
45
500
0.3
0.7
1.0
1.4
1.7
2.0
2.4
2.7
3.1
3.40
(0.26/0.32)
(0.62/0.74)
(0.88/0.93)
(1.23/1.48 )
(1.50/1.80)
(1.76/1.86)
(2.11/2.23)
(2.38/2.85)
(2.72/2.87)
(2.99/3.60)6.8
6.5
6.0
5.8
5.4
5.1
4.8
4.4
4.1
3.7
3.4
(5.98/7.19)
(5.71/6.87)
(5.28/6.34)
( 5.1/6.13)
( 4.75/5.7)
(4.49/5.39)
(4.22/5.04)
(3.87/4.65)
( 3.6/4.33)
(3.26/3.91)
(2.99/3.59)
·Mixing ratio
Check the specific gravity of engine coolant in the
cooling system in temperature ranges from 0¡ C to
50¡ C using a suction type hydrometer, then
determine the density of the coolant by refering to the
table at left.
Page 1659 of 3573
ENGINE COOLING 6B Ð 5
ON-VEHICLE SERVICE
WATER PUMP
REMOVAL
Preparation
·Drain coolant.
1. P/S pump Drive Belts
·Loosen P/S pump mounting bolt, loosen adjust
bolts and remove the drive belts.
2. AC Generator Drive Belt
·Loosen AC Generator mounting bolt (bottom
side), adjust plate lock bolt, and remove the drive
belt.
3. Cooling Fan Assembly
·Remove lock nut and take out cooling fan
assembly, distance piece, and fan pulley.
4. Crankshaft Damper Pulley.
5. Gear Case Cover.
6. Water Pump Assembly
7. O-ring
INSPECTION
Make necessary repair and parts replacement if extreme
wear or damage is found during inspection. Should any
of the following problems occur, the entire water pump
assembly must be replaced.
·Cracks in the coolant pump body
·Coolant leakage from the seal unit
·Play or abnormal noise in the bearing
·Cracks or corrosion in the impeller
Page 1660 of 3573
6B Ð 6 ENGINE COOLING
INSTALLATION
7. O-ring
·Set O-ring in water pump body groove.
6. Water Pump Assembly
·Install water pump assembly, and tighten to
specified torque.
20(2.0/14)N·m (Kg·m/lb.ft)
5. Gear Case Cover
·Install gear case cover, and tighten to specified
torque.
8(0.8/69)N·m (Kg·m/lb·in)
4. Crankshaft Damper Pulley
·Install crankshaft damper pulley, and tighten to
specified torque.
3. Cooling Fan Assembly
·Install fan pulley, distance piece, and cooling fan
assembly in this order on water pump, and tighten
to specified torque.
19(1.9/14)N·m (Kg·m/lb·ft)
2. AC Generator Drive Belt
·Install AC Generator drive belt and adjust belt
tension.
·(Refer to Drive Belt Adjustment in this Section).
1. P/S Pump Drive Belts
·Install P/S pump drive belts and adjust belt
tension.
·(Refer to Drive Belt Adjustment in this Section).8(0.8/69)N·m (Kg·m/lb·in)
Page 1661 of 3573
ENGINE COOLING 6B Ð 7
THERMOSTAT
REMOVAL
Preparation
·Disconnect battery ground cable.
·Drain coolant from the radiator and engine.
1. Water Hose; Turbocharger (4JG2-T Only)
2. Outlet Pipe
·Remove mounting bolt and remove outlet pipe
together with radiator hose.
3. Gasket
4. Thermostat
INSPECTION
Submerge the thermostat assembly in the water.
Place wooden blocks on the bottom of the water
container.
Not to directly heat the thermostat.
Gradually increase the water temperature. Stir the water
so that the entire water is same temperature.
·Make sure that primary valve begins to open at the
specified temperature.
82 (180 )
°C (°F) Valve Opening Temperature
Page 1662 of 3573
6B Ð 8 ENGINE COOLING
·Make sure that secondary valve opens fully at the
specified temperature.
Make necessary repair and parts replacement if extreme
wear or damage is found during inspection.
INSTALLATION
4. Thermostat
3. Gasket
2. Outlet Pipe
·Connect outlet pipe and tighten bolts to the
specified torque.
19(1.9/14)
N·m (Kgm/lb·ft)
1. Water Hose: Turbocharger (4JG2-T Only)
·Install battery ground cable.
·Pour coolant,
·Start the engine and check coolant leakage.
95 (203)
°C (°F) Valve Full Open Temperature
Page 1663 of 3573
ENGINE COOLING 6B Ð 9
RADIATOR
REMOVAL
Preparation
·Disconnect battery ground cable.
·Loosen drain plug to drain coolant.
1. Radiator Hose
·Disconnect lower hose and upper hose from the
engine.
2. Fan Guide Lower
·Remove clips on both sides and the bottom lock.
3. Reservoir Tank Hose
·Disconnect the hose from radiator.
4. Bracket
5. Radiator Assembly
·Remove upward the radiator assembly with hose,
taking care not to damage the radiator core by fan
blade.
·Remove cushion rubbers on both sides of the
bottom.
INSPECTION
Radiator Cap
·Measure the valve opening pressure with the radiator
cap tester. Replace the radiator cap if it exceeds the
standard.
Check the condition of negative pressure valve in the
center of valve seat side of the cap. If the valve seat
does not move smoothly due to rust or dust, clean or
replace the radiator cap.
Valve opening pressure
93.3 – 122.7 (0.95 – 1.25/13.5 – 17.8)kPa(Kg/cm2 / psi)
Page 1664 of 3573

6B Ð 10 ENGINE COOLING
Radiator Core
·Deformed radiator fins could reduce radiation effects,
resulting in overheat. Straighten the fins. In such a
case, take care not to damage the fin roots.
·Remove dust and other foreign materials.
Flushing the Radiator
·Wash the inside of radiator and the coolant passage
with water and neutral detergent. Remove all scales
and rust.
Checking for Coolant Leakage
·Check the cooling system for leakage with the radiator
cap tester by applying 196.0kPa (28.4 psi) air pressure
from filler neck to inside the radiator.
INSTALLATION
5. Radiator Assembly
·Install cushion rubbers on both sides of radiator
bottom.
·Install radiator assembly with hose, taking care not
to damage the radiator core by a fan blade.
4. Bracket
·Support the radiator upper tank with the bracket
and fix the radiator.
3. Reserve Tank Hose
2. Fan Guide, Lower
1. Radiator Hose
·Connect inlet hose and outlet hose to the engine.
·Connect battery ground cable.
·Pour coolant
·Pour coolant up to filler neck of radiator, and up to
MAX mark of reserve tank.
·Start engine to warm up, and check for coolant
level. Replenish coolant if it does not reach the
radiator filler neck, and tighten the cap completely.