Zontes ZT350T-D, Maintenance Manual, Page: 109 / 152

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5.2 Failure phenomenon
When the water temperature gauge indicates high, the engine temperature is overheated, but the
coolant temperature in the water tank is not high, it is not hot when touching the radiator by hand,
and the small water tank fan rotates normally. It indicates that the big circulation is blocked or
blocked, which can be preliminarily judged as abnormal thermostat.
There are generally two cases of abnormal thermostat:
a. The main valve is closed for a long time, and the coolant is circulated in a small circulation route
regardless of the water temperature, which causes the engine to overheat.
b. The main valve is in the open state for a long time, and the phenomenon is that the water
temperature rises slowly when starting, especially in winter, the slow rise of the coolant temperature
makes the engine not work at the normal temperature, and the engine temperature is too low.
5.3 Disassembly
Checking method of thermostat assembly:
Seal the two ports, pass in compressed air of 181 kPa (1.85 Kgf/cm2, 26.3 psi) from the other port, put it in the water and let it
stand to see if there are bubbles, if there is leakage.
1-M6×10 bolt*2 2-M6×12 bolt 3-φ5.6×φ1O ring 4-thermostat upper shell 5-thermostat core 6-thermostat lower shell
5.4 Thermostat core inspection
Check the opening temperature, full opening temperature and lift of the main valve in the thermostatic heating equipment
with adjustable temperature. If one of them does not meet the specified value, it should be replaced. Or use a thermometer,
water, heater, and container to test.
The initial opening temperature of the thermostat is 80
～
84
℃
(176
～
183 F), and the core moving 0.1mm (0.004 in) can be
regarded as the initial opening. The full opening temperature is 95°C (203 F), and the core movement is greater than 3.5mm
(0.14 in).
The simple test method is to put the core body into a high temperature resistant container, pour it into boiling water and soak
for a period of time, take out the core body with pliers, and observe whether the valve can be fully opened. Until all closed.
The joint surface should be cleaned before rematching, and no O-ring should be installed.
6. Water pipe
Check whether there are cracks, bulges and other defects on the surface of each water pipe. Block one end of the water pipe,
ventilate the other end and put the water pipe into the nozzle to check if there is any air bubbles, if any, replace it.
7. Check the water pump cover assembly
Check the two points indicated by the arrows for leakage.
The bolts are for cooling liquid bolts. If there is leakage,
remove the bolts and replace the O-ring. If there is leakage
at the leaking pipe of the right crankcase cover, you can try
to remove the leaking pipe (because the sealant is applied
before press-fitting, it is difficult to pull out), clean it up,
reapply the sealant and reinstall it; or directly replace the
right crankshaft Box cover assembly.
A small amount of coolant leaking from the leaking pipe is
normal. If the engine is running continuously, it is abnormal.
The water pump cover needs to be disassembled to check
whether the seal has failed.