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Shangchai SC27G Series Abnormal Troubles

Jan. 03, 2018

This is the part three for Shangchai SC27G series diesel engine troubleshooting guidelines. At the previous parts, the problem of engine will not start, engine power output low, abnormal noise, vibration and smoke are solved. This section mainly focus on troubleshooting the problem of abnormal oil pressure, oil temperature and consumption too high and coolant temperature too high.

Shangchai SC27G Series Abnormal Troubles


(5) Abnormal Oil Pressure


Fault feature



Possible cause




Oil pressure decrease and if can not be corrected by the pressure regulating valve and the reading of the pressure gauge fluctuates.



(1) Oil leak at the oil pipeline.


(2) Air in the oil pump, or inefficient oil filter, fracture of the cooler core, or oil leak at the oil seal gasket.


(3) Block of the oil cooler or oil filter, fracture of the cooler core, or oil leak at the oil



(4) Bad oil leak at the crankshaft bearings, crankshaft front and rear oil seals, camshaft bearings, connecting rod bearings, rocker arm shafts or rocker arms.


(5) Fuel in oil.


(6) The piston cooling jet(s) is not installed.


(7) Oil is diluted.



Check and tighten the nuts.


Add oil to the defined level.


Clean the oil cooler, and replace damaged parts and oil filter if necessary.


Check each part, and replace those whose wear exceeds the defined value.


Find out the location of fuel entering oil and make necessary repair. Change the oil and oil filter.


Install the missing piston cooling jets.


Find the cause and change the oil and oil filter.



No oil pressure, the indicator of the pressure of the pressure gauge keeps standstill.



(1) The oil pressure gauge is damaged.


(2) Block of the oil duct.


(3) Serious damage or seizure of the oil pump due to incorrect assembly.


(4) Oil pressure regulating valve does not work due to the damage of its spring.



Make replacement.


Clean the oil duct.


Reinstall the oil pump and replace it if required.


Replace the regulating valve.


(5) Oil Temperature And Consumption Too High


Fault feature



Possible cause





The reading of oil temperature gauge exceeds the defined value, and still be after the enhancement of cooling.


Meanwhile, there is black smoke from the exhaust pipe.


(1) Overload of the engine.


(2) The reading of the themometer is incorrect.


(3) Oil level is too low or too high.


(4) Insufficient cooling water or fan wind flow.


(5) Block of the cooler.



Decrease load.


Regulate the themometer and replace it when require.


Add lube oil to the defined level.


Pay attention to keep smooth flow of coolant and regulate the belt tension to reach the defined speed of the water pump and fan.


Clean the oil cooler.





The oil level decreases rapidly, and the oil color is black. There is white smoke at the oil filter port and ventilation pipe, and blue smoke from the exhaust pipe.



(1) Low-load running for a long time.


(2) The specification of used oil is not correct.


(3) The failure of the elastic seal of the turbocharger.


(4) The oil return hole of the piston oil ring is block by carbon deposit.


(5) The seizure or serious wear of the piston ring(s) or/and over wear of cylinder liner leads to oil into combustion chamber and the combustion gas into the crankshaft case.


(6) Wear of valve guides.




Enhance load to a proper degree.


Choose oil according to the defined specification in this manual.


Let a professional serviceman repair the turbocharger. Make replacement if necessary.


Clean off the carbon deposit and replace the oil rings if necessary.


Replace the piston rings, and replace the cylinder liners if necessary.


Repair the valve guides and make replacement if required.


(7) Coolant in lube oil



Fault feature



Possible cause







There is yellow bubble in oil, and coolant steam condenses on the surface of the crankcase ventilation pipe.




Coolant leak due to the damage of the cylinder liner seals.


Change the liner seals.


Coolant leak at the contacting planes of the cylinder line and cylinder block.



Check the contacting planes for flatness and the gasket for damage, and make replacement if necessary.



Coolant leak due to cavitation in the cylinder liner.



Change the liner.


Coolant leak due to the damage of the cylinder head gasket.



Change the head gasket.



Mixture of oil and coolant due to the damage of the oil cooler core.



Check the cooler core and replace it if necessary.


Coolant into the oil pan:

(1) Coolant leak at the water pump shaft seal ring.


(2) Damage of the water seal ring of the water pump.





Check the water pump, and replace the water pump if necessary.


Replace the water pump.


Coolant leak due to the cylinder block cavitation (especially at the side of the push rods).



Change the cylinder block.


(8) Coolant temperature too high



Fault feature



Possible cause





There is no or less coolant from the engine, and coolant temperature increase continually after the engine has started up.




There is air in the cooling system.



Loosen the air bleed joint on the water pipe, discharge the air until the smooth flow of the outlet coolant, and tighten all joints of the water pipeline.



The temperature of the coolant is too high under high-load and the oil temperature also increases.




(1) The speed of the water pump or fan can not reach the defined value.


(2) Not enough coolant in the cooling system.


(3) Malfunction of the pressure cap of the radiator.

(4) Block of the water pipeline.


(5) There are too many scale on the surface of the radiator.


(6) Incorrect water temperature gauge.


(7) Failure of thermostat.


(8) The clearance between the impeller and housing of the water pump is too large.


(9) The water pump impeller is damaged.



Adjust the belt tension to the defined value.


Add coolant to the defined level.


Check the pressure cap for function and replace it if required.


Clean the water pipeline.


Check the water temperature gauge, and replace it if necessary.


Check whether the opening and close temperatures of the thermostat are correct, and replace the thermostat if necessary.


Replace the water pump.


Replace the water pump.




The coolant in radiator is bubbing.




There is crack at the shoulder of the cylinder lines.



Replace the water liners.




For the information about Shangchai G series diesel engine operation and maintenance, please visit:

Shangchai G Series Diesel Engine Operation And Maintenance Manual

Shangchai G Series Engine Nameplate And Specifications

SC27G Diesel Engine installation and Connection

SC27G Diesel Engine Operation And Engine Start

SC27G Diesel Engine Maintenance Instructions

SC27G Diesel Engine Maintenance


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