Diesel engine lubrication system would, during engine operation, continuously deliver sufficient quantityof clean lubricating oil to the friction surface of all transmission parts where the oil film would form, realize liquid friction, reduce friction resistance, power consumption and machine parts worn, in further improve engine operation reliability and durability. Pressure lubrication, splash lubrication and grease lubrication may be selected dependent on the working conditions for each transmission part.

Lubrication system failure would cause poor lubrication for friction pair, give rise to increased friction heat and deteriorated friction wear, even severe mechanical accidents such as bearing enclasping and burnout. Common faults and reasons are presented below.

I. Abnormal engine oil pressure

Lubrication oil pressure would directly affect oil supply for lubrication points and also the bearing capacity of oil film. Engine oil pressure in main gallery of diesel engine is generally 0.20～0.40MPa and, when lower than 0.05MPa, effective lubrication would be impossible for each parts. Abnormal oil pressure is mainly manifested by excessive high and low pressure.

a. Reasons for excessivehigh oil pressure
Oil channel blockage may cause no lubricating oil supplied to some positions;
Excessively high oil viscosity would give rise to unsmooth flow and insufficient quantity;
Fine filter is dirty and bypass oil quantity is small;
Improper pressure adjustmentof pressure regulating valve or blockage and stagnation.

b. Reasons for excessivelow oil pressure
Low oil viscosity and large leakage at lubrication point; 
Excessive large fit clearance among lubrication parts gives rise to increased oil leakage, for instance, the engine oil pressure would be roughly reduced about 0.01MPa if the crankshaft main bearing clearance is creased every 0.01mm. 

-Improper adjustmentof pressure regulating valve;
-Fine filter element seal ring is failed, engine oil bypass quantity is increased; 
-Engine oil cooler is failed, and oil is permeated in water;
-Less oil quantity in oil pan and air in engine oil pump;
-Pipeline leakage.

II. Abnormal engine oil temperature

Normal engine oil temperature should be 90～110℃,and excessive high oil temperature would cause lower oil viscosity and reduced oil pressure, failure to form oil film; excessive low oil temperature would cause increased oil viscosity, poor mobility and increased friction resistance, increasing engine power loss.

1. Reasons for excessive high oil temperature
-Insufficient engine oil;
-Poor cooling performance, insufficient cooling water or air volume, or increased incrustation on internal water wall in cooler, water flow is blocked and, since incrustation is poor heat conductor, the heat from engine oil cannot be easily transmitted to cooling water;
-Low overflow valve pressure causes excessive overflow and less engine oil through cooler; 
-Improper fit clearance at each lubrication point causes failure to form rational oil film and increased friction heat;
-Diesel engine under long-term overload operation.

2.Reasons for excessive low oil temperature
-Insufficient engine oil;
-Poor cooling performance, insufficient cooling water or air volume, or increased incrustation on internal water wall in cooler, water flow is blocked and, since incrustation is poor heat conductor, the heat from engine oil cannot be easily transmitted to cooling water;
-Low overflow valve pressure causes excessive overflow and less engine oil through cooler; 
-Improper fit clearance at each lubrication point causes failure to form rational oil film and increased friction heat;
-Diesel engine under long-term overload operation.

III. High engine oil consumption

Reduced engine power, rapid reduced engine oil level in oil pan and exhaust with blue smoke are generally caused by oil seal or liner leakage or excessive wear of cylinder wall, specifically because of:

-Excessive large clearance betweenpiston and cylinder wall;
-Poor elasticity of piston ring, particularly oil ring; 
-Cylinder sleeve and piston ring is excessively worn, piston ring is stuck or Torsional ring is inversely installed;
-Excessive large side and edge clearancebetween piston ring and ring groove, or the oil return hole of upper oil ring on piston is blocked by carbon deposit;

-Supercharged diesel engine turbocharger’s elastic sealing device is failed;
-Excessive large clearance between valve rod and conduit or oil seal is failed.


IV. Oil-water mixed

Cooling water enters engine oil, and the oil then becomes deteriorated, turns into milk white, has its viscosity reduced or failed, causing poor lubrication performance; engine oil would also enter cooling water to mix with incrustation and other impurities, forming thick mixture on the top of water tank.

Reasons for oil-water mixture:
①Pipes in engine oil cooler is broken, or the seal ring on both ends of cooler core is failed, causing engine oil to mix with water in cooler;
②Water channel rubber gasket on the external wall of cylinder sleeve has lost sealing performance due to aging, cooling water around cylinder sleeve enters oil pan;
③Water seal ring or oil seal ring on cylinder mattress become failed;
④Cylinder or cylinder cover is cracked, and water enters oil pan.

V. Rapid engine oil deterioration

Generally engine oil shall be replace after every 500h operation for diesel engine, but it cannot be used after a relatively short time since it has become thinner and impurity quantity is increased.

Main reasons for engine oil deterioration:

-Incorrect engine oil grade, poor quality; engine oil above CC grade shall be selected for diesel engine with supercharge and rated speed higher than 2,000r/min;
-Diesel engine is under poor condition, subject to gas carry-over, oil leakage, excessive large fit clearance or high oil temperature;
-Diesel engine usually operates under low temperature, low load or speed, subject to insufficient piston distortion and incomplete combustion, diesel enters oil pan along with cylinder wall, engine oil therefore becomes thinner and deteriorated;
-Waste gas entering oil pan condensates into moisture and acid matters, causing engine oil deteriorated;
-Engine oil filter becomes dirty, unfiltered dirty engine oil comes to lubrication point, accelerating parts wear;
-Internal leakage is caused by filter seal ring breakage, some engine oil would directly enter filter without through filter element, causing engine oil deteriorated.