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  4. PART 1 MODERN EXHAUST GAS TREATMENT SYSTEMS AND THE LOSS OF REQUIRED ENGINE OIL PROPERTIES

PART 1: MODERN EXHAUST GAS CLEANING SYSTEMS AND LOSS OF REQUIRED ENGINE OIL PROPERTIES EXHAUST GAS RECIRCULATION (EGR) AND THE ISSUE OF OIL THERMAL DEGRADATION

1. Introduction and basics

It is obvious to most people who are familiar with how a car engine works that improper operation of the drive unit along with its sensors and actuating elements may lead to exhaust gas cleaning system failure. There are numerous examples of such failure of the engine and engine management system. Let us name some of the most common ones: mechanical wear and tear (engine oil consumption and burning), injection system (e.g. damaged, improperly coded or out-of-tolerance injectors), damaged turbocharger (improper setting of wastegate actuator, variable VNG geometry), air-mass meter and/or boost pressure sensor disfunction, faulty electrical connections, etc.  


It would be interesting to follow the reversal of the primary occurrence. Can exhaust gas cleaning system failure lead to engine failure? Can engine oil be a vector which, in the event of exhaust gas cleaning system failure, may lead to engine failure under extreme conditions?  


As this is not immediately obvious, we suggest an answer to this question later on. 


To better understand key concepts, we recommend completing the course on lubrication and lubricants, which is available on the Learning Campus, a free Castrol e-learning platform: 


https://thelearningcampus.bp.com/uxp/login 


After learning the basic principles, we can proceed to the next chapter. If you want to refresh what has been covered, you can refer to this short review. 
The first part of Castrol’s training for partners concerns car engine oils. In this we learn that the basic function of a lubricant is to decrease friction, wear and tear; however, it also needs to fulfil many other functions (e.g. preventing surface corrosion, cooling the engine, preventing contaminant accumulation and retaining it within the suspension, keeping surfaces clean, sealing the combustion chamber, etc.). 


Remember that engine oil is required to fulfil many functions simultaneously in order to ensure the efficient, long-term operation of the engine without it deteriorating and without having a negative impact on the environment. 


The different functions of engine oil correlate to its individual components.  


For example, keeping the engine components (in particular, the pistons and piston rings) clean, and retaining contaminants (oxides, wax, paint and sediment) within the suspension are functions that are only supported by additives called detergents and dispersants.  

In the previous article we discussed the relation between the diesel particulate filter and the loss of engine oil viscosity. Now we are going to look at exhaust gas recirculation (EGR) and oil thermal breakdown as part of the same event – the modern exhaust gas cleaning system and loss of engine oil properties. 

2. What happens to engine oil during use?

During the time that the oil is in use (between oil changes), it can become contaminated by different substances (such as fuel, particles created by the wear and tear of metal parts, oxides, acids, water, etc.). 


These contaminants can cause physical and chemical changes to occur in the lubricant which in turn may lead to a certain degree of viscosity index loss or thermal fatigue. If these changes are serious enough, they can lead to viscosity-related or thermal oil breakdown which may in turn lead to problems with engine operation – and ultimately its failure.  


Oil breakdown is an occurrence generated mainly by the dilution of oil with fuel and constant polymer shearing stresses (which cause the long bonds between particles to break), which we discussed in the previous article.  


Thermal breakdown is basically a change of engine oil properties caused by excessive heat in the engine, and it seriously decreases the capacity of the oil to maintain a protective oil film. This process is intensified by the presence of contaminants in the oil


There are three main types of thermal damage: oil thickening (viscosity increase), formation of sludge, wax and carbon sediment, and an increase of the amount of oil burnt in the engine.

Fig. 1a Oil thickening (increase in viscosity)
Fig. 1a Oil thickening (increase in viscosity) 
Formation of sludge sediment and Formation of sediment in the form of wax and charring

Which engine control system operation irregularities can cause thermal overstress of the oil and fatigue?  


Failure of one of the cooling system components (water pump, blocked cooler, clogged thermostat) would be an obvious answer.  


Sometimes the failure is the result of incorrect procedures applied as a part of service activities. 


When the coolant pump is replaced, the circuit should be rinsed using the old pump and the coolant should be changed. If a workshop proceeds directly to dismounting the pump and topping up the leaking liquid, a significant amount of degraded liquid can remain in the system, which can have an irreversible impact (e.g. the risk of damaging the pump unit seals). 
 
When a coolant pump is supplied with a seal (regardless of its material), it is strictly forbidden to apply sealing compound!

Fig. 2a Coolant pump installed using sealing compound
Fig. 2a Coolant pump installed using sealing compound 
Fig. 2b Coolant pump installed using a large amount of sealing compound
Fig. 2b Coolant pump installed using a large amount of sealing compound 
Poor workshop practice is sometimes revealed by the use of sealing compound in such large amounts that it has blocked the rotation of the coolant pump blades. 
Fig. 3 a, b, c. After adding a very large amount of sealing paste, the rotor became pasted to the body of the pump. Consequently the rotor broke off of the drive shaft when the engine was started, causing irreversible damage to the component.
Fig. 3 a, b, c. After adding a very large amount of sealing paste, the rotor became pasted to the body of the pump. Consequently the rotor broke off of the drive shaft when the engine was started, causing irreversible damage to the component. 
Adding a very large amount of sealing paste prevents the coolant pump from working at an optimum level (at which the remaining components driven by the belt are located); as a result, additional stresses occur on the pump shaft and quickly cause damage to the bearings and internal sealing members (rolling noise, liquid leakage, thermal overstress). 
Figure 4. Explanation of pump operation in relation to the other components driven by the toothed belt after a large amount of sealing paste is added.
Figure 4. Explanation of pump operation in relation to the other components driven by the toothed belt after a large amount of sealing paste is added. 
Cooling systems have evolved to such an extent that nowadays significantly more complicated systems can be found, including some that use several pumps for one engine (powered both mechanically and electrically), electrically supported thermostats and various electromagnetic valves. 
Fig. 5a Liquid pump with electric valve and Fig. 5b Electric coolant pump  and  Fig. 5c Thermostat and Fig. 5d Assembly of pump, thermostat and regulator

Error codes that can be read by diagnostic tester may now be available for some of these new and complicated systems.  


Engine oil thermal overstress can be caused by many other malfunctions, including temperature sensor damage, engine operation with an incorrect mix of fuel and air, incorrect spark advance, etc.  


In the next section we will try to answer the following question: Can EGR system failure cause engine overheating and engine oil thermal fatigue? 
 
Please continue to the second part of this text where we will discuss the EGR valve and engine oil thermal decomposition.