
RENR9968-02 47
Testing and Adjusting Section
Cooling System
i02630833
Cooling System - Check
(Overheating)
SMCS Code: 1350-535
Above norm a l coolant temper atures can b e caused
by many conditions. Use the following procedure
to determine the cause of above normal coolant
temperatures:
Personal injury can result from escaping fluid un-
der pressure.
If a pressure indication is shown on the indicator,
push the release valve in order to relieve pressure
before removing any hose from the radiator.
1. Check the coolant level in the cooling system.
Refer to Operation and Maintenance Manual,
“Cooling System Coolant Level - Check”. If the
coolant level is too low, a ir will g et into the cooling
system. Air in the cooling system will cause a
reduction in coolant fl ow and bubbles in the
coolant. Air bubbles will keep coolant away from
the engine parts, which will prevent the transfer of
heat to the coolant. Low coolant level is caused by
leaks or inc orrectly filling the radia to r.
2. Check the mixture of antifreeze and water. The
mixture s hould be approximately 50 percent
water and 50 percent antifreeze with 3 to 6
percent coolant conditioner. Refer to Operation
and Maintenance Manual, “Refill Capacities and
Recommendations”. If the coolant mixture is
incorrect, drain the system. Put the correct mixture
of water, antifreeze and coolant conditioner in the
cooling system.
3. Check for air in the cooling system. Air can enter
thecoolingsystemindifferentways.Themost
common caus es of air in the cooling syste m
are not filling the co o ling system correctly and
combustion gas leakage into the cooling system.
Combustion gas can get into the system through
inside cracks, 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 c oolant. Air bubbles keep coolant
away from the engine parts, which prevents the
transfer of heat to the coolant.
4. Check the fan clutch. A fan clutch that is not
turning at the correct speed can cause improper
air speed across the radiator core. The lack of
proper air flow across the radiato r core can cause
the coolant not to cool to the proper temperature
differential.
5. Check the water temperature gauge. A water
temperature gauge which does not work correctly
will not show the correct temperature. Refer to
Testing and Ad ju sting, “Cooling S ystem - In sp ect”.
6. Check the sending unit. In some conditions, the
temperature sensor in the engine sends signals to
a sending unit. The sending unit converts these
signals to an electrical impulse which is used by a
mounted gauge. If the sending unit malfunctions,
the gauge 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.
a. Check the radiator for a restriction to coolant
flow. Check the radiator for debris, dirt, or
deposits on the inside of the radiator core.
Debris, dirt, or deposits will restrict the flow of
coolant through the radiator.
b. Check for debris or damage between the fins
of the radiator core. Debris between the fins of
the radiator core restricts air flow through the
radiator core. Refer to Testing and Adjusting,
“Cooling Syste m - Inspect”.
c. Ensure that the radiator size is according to
the specifications of the Original Equipment
Manufacturer (OEM). An undersized radiator
does not have enough area for the effective
release of heat. This may cause the engine to
run at a temperature that is hig her than normal.
The normal temperature is dependent on the
ambient temperature.
8. Check the filler cap. A pressure drop in the radiator
can cause the boiling p o int to be lower. This can
cause the cooling system to boil. Refer to Testing
and Adjusting, “Cooling S ystem - Test”.
9. Check the fan and/or the fan shroud.
a. The fan must be large enough to send air
through most of the area of the radiator
core. Ensure that the size of the fan and the
position of the fan are according to the O EM
speci
fications.
b. The fa n shroud must be the proper size and
the fan shroud must be positioned correctly.
Ensure that the size of the fan shroud and the
position of the fan shroud are according to the
OEM specifications.