Isuzu N-Series. Manual - part 377

6B-2 ENGINE COOLING

GENERAL DESCRIPTION

The engine cooling system consists of the radiator, the
water pump, the cooling fan, and the thermostats.
To quickly increase cold engine coolant temperature for
smooth engine operation, the coolant is circulated by the
water pump and thermostats through the by-pass hose
and back to the cylinder body. The coolant does not cir-
culate through the radiator.
When the coolant temperature reaches 82

°C (180°F),

the thermostat will begin to open and a gradually in-
creasing amount of coolant will circulate through the ra-
diator.
The thermostats will be fully open when the coolant tem-
perature reaches 100

°C (212°F). All of the coolant is

now circulating through the radiator for effective engine
cooling.
Engine coolant change procedure.

1. To change engine coolant, make sure that the en-

gine is cool.

Warning:

WARNING:
WHEN THE COOLANT IS HEATED TO A HIGH TEM-
PERATURE, BE SURE NOT TO LOOSEN OR RE-
MOVE THE RADIATOR CAP. OTHERWISE YOU
MIGHT GET SCALDED BY HOT VAPOR OR BOILING
WATER. TO OPEN THE RADIATOR CAP, PUT A
PIECE OF THICK CLOTH ON THE CAP AND LOOS-
EN THE CAP SLOWLY TO REDUCE THE PRESSURE
WHEN THE COOLANT HAS BECOME COOLER.

2. Open radiator cap and drain the cooling system by

loosening the drain valve on the radiator and on the
cylinder body.

Notice:
For best result it is suggested that the engine cooling
system be flushed at least once a year.

Legend

1. Reservoir tank

8. Air bleeding

2. Radiator cap

9. Water outlet pipe

3. Bypass hose

10. Thermostat

4. Radiator

11. Thermometer unit

5. Drain cock

12. Water jacket

6. Cooling fan

13. Oil cooler

7. Water pump

N6A0789E

ENGINE COOLING 6B-3

It is advisable to flash the interior of the cooling system
including the radiator before using anti-freeze (ethylene-
glycol based).
Replace damaged rubber hoses as the engine anti-
freeze coolant is liable to leak out even minor cracks.
Isuzu recommends to use Isuzu genuine anti-freeze
(ethylene-glycol based) or equivalent, for the cooling
system and not add any inhibitors or additives.

Caution:
A failure to correctly fill the engine cooling system in
changing or topping up coolant may sometimes cause
the coolant to overflow from the filler neck even before
the engine and radiator are completely full.
If the engine runs under this condition, shortage of cool-
ant may possibly result in engine overheating. To avoid
such trouble, the following precautions should be taken
in filling the system.

3. To refill engine coolant, pour coolant up to filler

neck using a filling hose which is smaller in outside
diameter of the filler neck. Otherwise air between
the filler neck and the filling hose will block entry,
preventing the system from completely filling up.

4. Keep a filling rate of 9 liter/min or less. Filling over

this maximum rate may force air inside the engine
and radiator.
And also, the coolant overflow will increase, mak-
ing it difficult to determine, whether or not the sys-
tem is completely full.

5. After filling the system to the full, pull out the filling

hose and check to see if air trapped in the system
is dislodged and the coolant level goes down.
Should the coolant level go down, repeat topping-
up until there is no more drop in the coolant level.

6. After directly filling the radiator, fill the reservoir to

the maximum level.

7. Install and tighten radiator cap and start the en-

gine. After idling for 2 to 3 minutes, stop the engine
and reopen radiator cap. If the water level is lower,
replenish.

Warning:

8. After tightening radiator cap, warm up the engine at

about 2,000 rpm.
Set heater adjustment to the highest temperature
position, and let the coolant circulate also into heat-
er water system.

9. Check to see the thermostat has opened through

the needle position of water thermometer, conduct
a 5-minute idling again and stop the engine.

10. When the engine has been cooled, check filler

neck for water level and replenish if required.
Should extreme shortage of coolant is found,
check the coolant system and reservoir tank hose
for leakage.

11. Fill the coolant into the reservoir tank up to “MAX”

line.

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 outlet pipe.

Legend

A. Without jiggle valve

N6A0790E

N6A0791E

6B-4 ENGINE COOLING

Radiator

The radiator is a tube type with corrugated fins. In order
to raise the boiling point of coolant, the radiator is adjust-
ed through a valve fitted to the upper tank to a pressure
range of 93 — 123 kPa (0.95 — 1.25 kg/cm

). The cap

fitted to the cylinder head thermostat housing has only a
water supply function.

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 referring
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

Notice:
Anti-freeze solution + Water = Total cooling system ca-
pacity.

In case of 12 lit (3.17 US gal/2.64 UK gal) total cooling system capacity

Legend

A. With jiggle valve

N6A0792E

N6A0793E

Legend

1. Freezing point
2. Mixing ratio

Mixing ratio

Anti-freeze solution (Lit/qt.)

Anti-freeze solution (Lit/qt.) + water (Lit/qt.)

N6A1645E

Freezing point:

°C (°F)

Mixing ratio: %

Anti-freeze solution:

L (Imp.qt./U.S.qt)

Water:

L (Imp.qt/U.S. qt)

-18 (4)

4.2 (4.44/3.70)

7.8 (8.24/6.86)

-25 (-13)

5.0 (5.29/4.40)

7.0 (7.40/6.16)

-35 (-31)

6.0 (6.34/5.28)

-40 (-40)

6.4 (6.76/5.63)

5.6 (5.92/4.93)

ENGINE COOLING 6B-5

• Mixing ratio

Check the specific gravity of engine coolant in the
cooling system in temperature ranges from 0 —
50

°C (32 — 122°F) using a suction type hydrome-

ter, then determine the mixing ratio of the coolant
by referring to the table.

Legend

1. Specific gravity
2. Coolant temperature
3. Mixing ratio

N6A1646E

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