Maintenance of Major Components
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Replacing thermostat and precautions for handling
(1) Precautions for handling
The wax pallet type thermostat does not react as quickly as bellows type one to a variation of
temperature of coolant. Such relatively slow reaction is mainly due to the large heat capacity of
the wax pellet type thermostat. Therefore, to avoid a sharp rise of coolant temperature, it is
essential to idle the engine sufficiently before running it. In cold weather, do not run the engine at
overload or over-speed it immediately after engine starting
(2) When draining out or replenishing coolant, do it slowly so that air is bled sufficiently from the
entire cooling system.
(3) Replacing thermostat
If the thermostat is detected defective, retrace with a new one.
5.2.3. Diagnostics and troubleshooting
Complaints Possible causes Corrections
1. Engine overheating
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Lack of coolant
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Replenish coolant
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Radiator cap pressure valve spring
weakened
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Replace cap
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Fan belt loosened or broken
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Adjust or replace fan belt
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Fan belt fouled with oil
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Replace fan belt
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Thermostat inoperative
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Replace thermostat
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Water pump defective
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Repair or replace
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Restrictions in water passages due to
deposit of scales
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Clean radiator and water
passages
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Injection timing incorrect
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Adjust injection timing correctly
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Restriction in radiator core
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Clean exterior of radiator
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Gases leaking into water jacket due to
broken cylinder head gasket
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Replace cylinder head gasket
2. Engine overcooling
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Thermostat inoperative
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Replace thermostat
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Ambient temperature too low
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Install radiator curtain
3. Lack of coolant
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Radiator leaky
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Correct or replace
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Radiator hoses loosely connected or
damaged
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Retighten clamps or replace
hoses
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Radiator cap valve spring weakened
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Replace cap
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Water pump leaky
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Repair or replace
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Heater hoses loosely connected or
broken
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Tighten or replace hoses
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Cylinder head gasket leaky
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Replace cylinder head gasket
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Cylinder head or cylinder block cracked
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Replace cylinder head block
4. Cooling system noisy
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Water pump bearing defective
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Replace bearing
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Fan loosely fitted or bent
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Retighten or replace fan
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Fan out of balance
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Replace fan
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Fan belt defective
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Replace fan belt
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