User Manual

46 SENR9977
Testing and Adjusting Section
Cooling System
i02274237
Cooling System - Check
(Overheating)
Above normal c
oolant temperatures can be caused
by many conditions. Use the following procedure
to determine the cause of above normal coolant
temperature
s:
1. Check the coolant level in the cooling system. If
the coolant l
evel is too low, air will get into the
cooling system. Air in t he cooling system w ill
cause a reduction in coolant flow and bubbles
in the coola
nt. Air bubbles will keep the coolant
away from the engine parts, which will prevent the
transfer of heat to the coolant. Low coolant level is
caused by le
aks or incorrectly filling the expansion
tank.
2. Check that
the exterior of the radiator is not
blocked with debris.
3. Check that
the drive belts are not loose. Refer to
Testing and Adjusting, “V-Belt - Test”.
4. Check that
the fan is correctly installed and that
the fan is not damaged.
5. Check for a
ir in the cooling system. Air can enter
the cooling system in different ways. The most
common causes of air in the cooling system
are not fi
lling the cooling system correctly and
combustion gas leakage into the cooling system.
Combustion gas can get into the system through
inside cr
acks, a damaged cylinder head, or
a damaged cylinder head gasket. Air in the
cooling system causes a reduction in coolant
flow and
bubbles in the coolant. Air bubbles keep
the coolant away from the engine parts, which
prevents the transfer of heat to the coolant.
6. Check the sending unit. In some conditions, the
temperature sensor in the engine sends signals
toasen
ding unit. The sending unit converts these
signals to an electrical impulse which is used by a
mounted gauge. If the sending unit malfunctions,
the gau
ge can show an incorrect reading. Also if
the electric wire breaks or if the electric wire shorts
out, the gauge can show an incorrect reading.
7. Check the radiator for a restriction to coolant flow.
Check the radiator for debris, dirt, or deposits on
the in
side of the core. Debris, dirt, or deposits will
restrict the flow of coolant through the radiator.
8. Check the filler cap. A pressure drop in the cooling
system can caus
e the boiling point to be lower.
This can cause the cooling system to boil. Refer
to Testing and Adjusting, “Cooling System - Test”.
9. Check the cooling system hoses and clamps.
Damaged hoses with leaks can normally be seen.
Hoses that ha
ve no visual leaks can soften during
operation. The soft areas of the hose can become
kinked or crushed during operation. These areas
of the hose ca
n cause a restriction in the coolant
flow. Hoses become soft and/or get cracks
after a period of time. The inside of a hose can
deteriorat
e, and the loose particles of the hose
can cause a restriction of the coolant flow.
10. Check for a r
estriction in the air inlet system. A
restriction of the air that is coming into the engine
can cause high cylinder temperatures. High
cylinder te
mperatures require higher than normal
temperatures in the cooling system.
11. Check for a
restriction in the exhaust system.
A restriction of the air that is coming out of the
engine can cause high cylinder temperatures.
a. Make a visual inspection of the exhaust system.
b. Check for d
amage to exhaust piping. Check for
damage to the exhaust elbow. If no damage
is found, check the exhaust system for a
restrict
ion.
12. Check the water temperature regulator. A water
temperat
ure regulator that does not open, or a
water temperature regulator that only opens part
of the way can cause overheating. Refer to Testing
and Adju
sting, “Water Temperature Regulator -
Te s t ”.
13. Check th
e water pump. A water pump with a
damaged impeller does not pump enough coolant
for correct engine cooling. Remove the water
pump and
check for damage to the impeller.
14. Consider high outside temperatures. When
outside
temperatures are too high for the rating
of the cooling system, there is not enough of
a temperature difference between the outside
air and
coolant temperatures. The maximum
temperature of the ambient air that enters the
engine should not exceed 50 °C (120 °F).
15. When a load that is applied to the engine is too
large, the engine rpm does not increase with an
incre
ase of fuel. This lower engine rpm causes
a reduction in coolant flow through the system.
This combination of less air and less coolant flow
durin
g high input of fuel will cause above normal
heating.