FleetWatch Online - 33-Lube Logic

As an engine-failure specialist, Patrick Swan of Aswan Consulting is kept busy analysing the casualties of modern trucking's maintanace oversights. Here he explains the role lubricating oil plays in the efficient running of a diesel engine. He also shares his views on how operators should go about ensuring lubricity does not become an expensive issue.

Today's truck engines can withstand incredible levels of abuse. OEMs releasing new engine models subject them to the harshest conditions imaginable to ensure those engines operate smoothly in varying conditions around the world. Engine reliability and robustness are crucial if warranty claims are to be avoided and the company reputation upheld.

Once the new engine enters the market, a new reality sets in - the task of maintaining that engine, a responsibility which falls squarely on the shoulders of the operator. Basic maintenance includes a host of disciplines, one of which being proper engine lubrication using an appropriate quality lubricant which is changed as specified by the OEM. Many South African operators fall far short in both these areas.

Acid attacks
Lubricant quality is specified by the OEM, but what does it mean? A lubricant is a blend of base oils and performance increasing chemicals, often called additives, which must never be confused with after-market additives. The major performance requirements of a crankcase lubricant are to; cool bearings and pistons by carrying heat away; keep components clean, particularly the piston rings, so that they seal effectively, and control deposits throughout the engine; help to seal the piston rings by forming a lubricant film between the rings and liners; reduce friction and wear through correct lubrication; neutralise strong acids formed in the engine; and prevent rust and corrosion.

Cooling, sealing and to an extent lubrication, are a factor of the base oil, but all other performance aspects are provided by the chemical additives, which are carefully formulated by the lubricant blender. For example NOx (nitrogen oxides) is formed during combustion, together with carbon dioxide, water vapour and sulphur oxides. When NOx and sulphur oxides combine with the water vapour, nitric and sulphuric acids may be formed. These are strong acids and will readily attack any metal present in modern engines.

Renew right
As with lubricant quality, the oil change period is also specified by the OEM. Any lubricant can only give proper protection as long as the complex blend of chemical additives remains in solution in the base oil and is able to fulfil its function.
These chemical additives are 'sacrificial' in that they are consumed in service performing functions. At the same time, the lubricant becomes heavily contaminated, mostly with blow-by from the combustion chamber. Contamination and chemical additive depletion are the major reasons for regular oil renewal. The OEM recommended drain periods will have been established using the appropriate quality lubricant.

After examining many engine failures, the reality today is that more and more operators are either not using appropriate quality lubricants, or are exceeding the OEM recommended service intervals, or both. The results are at best only an increase in engine blow-by, but may also be a failed crankshaft bearing. Any bearing can fail first and experience shows that it is more often a big end bearing.

Driver education
Another trend is that drivers seem to continue after a failure has initiated, until the vehicle cannot proceed any further. A big end failure is normally very audible, but if the driver continues the failure becomes more than just a knock, usually ending with a ventilated block as the conrod comes through.

Avoiding costly engine failure and rising fuel bills should entail a 'back to basics' approach by operators where OEM-recommended lubricant and service intervals are adhered to and driver training includes education on the subject of engine failure.

Lubricant related engine failure case studies

Abnormally short engine life is far too common in South Africa. Having examined many engine failures, a regular cause is extended drain periods or use of inferior lubricants. - Patrick Swan

Piston rings and blow-by
Strong acids are formed where water vapour from combustion condenses - in the ring zone, so when the lubricant begins to die the first components to be attacked are the rings. Ring corrosion looks like this:

As the rings wear they loose compression and oil consumption increases. This is a very common cause of excessive blow-by and increased oil consumption, particularly for engines older than about 250 000 km, which do not normally suffer from abnormal blow-by.

Crankshaft bearings
With good maintenance and records, engines should not fail in service, but will be taken out of service and reconditioned based on performance and oil consumption. However crankshaft bearing failures seem to be becoming more common, and typically occur anywhere from 500 000 km to 800 000 km on engines which would normally exceed a million km, and often operate to between 1.5 and 2 million km before overhaul.

Strong acids attack the inter-granular bearing matrix, which makes the bearing look very rough like this:

When the engine continues in service the loose islands of bearing material flake off, or are wiped off, often only leaving the bearing. Here is an example of bearings where the bearing material was weakened by corrosion, (Top right)

Here is another example of bearings where the material is flaking off.

Closer inspection of these bearings by microscope is seen in the following two photographs

Here it is easy to see how the inter-granular matrix has been attacked and wiped off during engine operation.
After the bearing begins to break up, pieces of bearing material come loose and may be imprinted on the bearing as seen here below.