Thermostat; Tension Of Fan Belt - Mitsubishi 4DQ50 Service Manual

then fill the system with fresh water and run the engine again for flushing.
Before and after the use of an antifreeze, be sure to flush radiator.
3) For engine that has rather intricate water piping for the equipment with oil
cooler or for other reason, open bleeding cocks on cooling system, each time
cooling water changed, to make sure that the piping is full in every part. If an
overheat noticed even when thermostat is functioning well, bleed
(~r
eliminate
air out of) the system.
4) If dust collected on fins, clean them by blowing compressed air or water on
them from fan to recover cooling efficiency. Don't try to remove foreign
matters with a wire or the like. Such a way of cleaning often makes scratches
or cuts in water pipes, hence leading to leakage.
5-2 Thermostat
Poor operation of thermostat will much affect the service life of the engine in the
long run. In case the engine overheats even when cooling system is full and fan working
well the probable cause is that thermostat has got stuck up and remains close. If, on the
contrary, long oreration should not raise water temperature up to the optimum level
(75°-85°Cl. thermostat is suspected to remain open from puncture. In either case,
check it and take necessary measures.
Thermostat is designed to start opening at 76°C and fully open at 90°C under
atmospheric pressure. Continuous operation on cold water will quicken wear of
cylinder liners and rings.
5-3 Tension of fan belt
1) Every 60H r of run, check the tension of fan belt, Optimum tension is such that
a press with a thumb at
mid-point between genera-
tor pulley and water .pump
pulley makes it slack about
12mm. Execessive tension
quickens wear of belt itself
and of water pump and
generator bearings, while
lack of tension makes it slip
and a consequential drop of
cooling efficiency will cause
1. Fan belt 2. Generator pulley 3. Water
pump 4. Adjusting plate 5. Lock bolt
Fig.3-36 Checking the tension of fan belt
an overheat. Continuous slipping does it damage, too.
2) Inspect fan belt at times to see it is not damaged. Keep it always free from oil,
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