Engine Evolution - Selecting The Correct Car Engine Oil
Part 2 of this article continues from where the changes in engines and engine oils from the 1980s to 2000 were discussed, to an exploration of the major car engine developments from the year 2000 to date. It is vital to make sure the correct engine oil is used, whether it is a new car under warranty or an older car out of warranty. Engine lubricant choice is very important as the engine oils used need to meet the precise requirements set by the engine design and Original Equipment Manufacturer (OEM) specifications.
Engine evolution from the year 2000 to 2010
During this period of automotive innovation, there was an increased focus on improvements to diesel engine designs.
Diesel Particulate Filters
During this period from the new millennium, diesel engines saw the introduction of diesel particulate filters (DPFs). These units are designed to filter out any harmful solid matter that may have been generated during the combustion process. For diesel engines of course we are referring to issues that both soot and ash can cause to this aftertreatment device.
The DPF unit is fitted to the exhaust system and collects the solid matter as the exhaust gases pass through it. The DPF unit has a pressure differential sensor that measures the working pressure across the filter. As the DPF becomes blocked with soot, the pressure drops. Once it reaches a minimum value, a regeneration cycle is initiated. The fuel system ‘over fuels’ and this excess burns off in the DPF causing it to hit a peak temperature of over 600oC. This ‘oxidises’ the carbon, converting it from a solid to carbon dioxide which is a gas. This flows from the DPF regenerating it.
However, DPFs are also sensitive to being blocked by ash generated when a small amount of oil is burned in the combustion chamber, as highlighted earlier when discussing AdBlue®. This ash remains in the DPF despite the regeneration cycle and eventually, it cannot return to a working pressure. The DPF becomes blocked. Once again, the engine management system will shut the engine down or provide limited power (limp mode).
The engine oil therefore must be formulated with the optimum level of active chemistry to protect the components, reduce the effects of soot and minimise ash formation to prevent the premature blocking of the DPF.
2010 and beyond….
From 2010 and beyond, the use of more complex filters and alternative power technologies were started to be employed to further reduce the levels of emissions produced by cars.
Gasoline Direct Injection
Gasoline Direct Injection (GDI) has appeared occasionally in the past but never reached the levels of engineering efficiency as required by today’s manufacturers. GDI has slowly replaced port injection in passenger cars with the goal of dramatically improving fuel efficiency and reducing emissions.
With port injection, the fuel is injected into the intake manifold and with the incoming air is then swept into the combustion chamber, mixing during this process. This is not very efficient. With GDI, the fuel is injected straight into the combustion chamber, at significantly higher pressures, creating better atomisation and ensuring a more efficient burn, improved power and reduced emissions.
GDI is a massive improvement to the performance of the engine, however, it can cause a phenomenon called Low-Speed Pre-Ignition (LSPI).
The issues of LSPI are caused when the high fuel pressure washes away the oil from the combustion chamber wall and the oil pools on the piston crown. This happens during the ‘induction’ stroke. As the piston moves back up the bore, and before it reaches the point where the spark plug ignites the mixture, the heat and increasing compression, catalysed by this oil/fuel combination, leads to pre-ignition of the fuel/air mixture. Fractions of a second later the spark plug ignites the rest of the mixture and then you have two energy fronts moving towards each other. As they collide, the shock wave can cause catastrophic damage to the engine.
The oil used in these engines must combat this issue of LSPI and therefore a whole new family of engine oil specifications has been developed. These engine oil formulations have restricted levels of certain types of chemistry, primarily calcium compounds, that can contribute to the likelihood of LSPI, particularly under hard acceleration in small powerful engines.
Gasoline Particulate Filters
In petrol engines, another side effect of improved combustion, by moving to higher pressures and with greater levels of atomisation is again the creation of soot. Like diesel engines, this soot must be removed before it gets out to the atmosphere where it may cause health and environmental issues. To achieve this, gasoline particulate filters (GPFs) are fitted. GPFs, like DPFs, are sensitive to the levels of ash generated from burning the engine oil. Therefore, car engine oils must be carefully formulated to ensure this doesn’t happen, but without compromising the protection of the engine components.
Hybrid engine technology
The biggest step change in the move towards reducing exhaust pipe emissions, particularly CO2, has been in the proliferation of hybrid vehicle technologies. There are many variations in a hybrid configuration, but in all instances, it is the intermittent use of the engine, usually a small petrol engine, that brings with it challenges.
When a car engine runs under normal circumstances (unless stop/start mode is active) it starts only once during a trip and gets turned off when the journey is complete. This gets a useful heat soak on the engine, which has the benefit of driving off any unburnt fuel or accumulated water and maximising fuel efficiency.
However, engines used in hybrid vehicles don’t have this luxury. Firstly, the engine may ‘kick in’ when the vehicle has reached high road speeds and it is required to either begin charging the battery or worse takeover altogether to drive the wheels. The engine oil must circulate rapidly to stop any wear occurring under potentially full load. For this reason, engine lubricants developed for this application tend to be low viscosity, for example: 0W-20, 0W-16 and even 0W-8.
Condensation that has built up in the airspaces in the crankcase may not get driven off if the engine then shuts down again before reaching its optimum operating temperature. The water will persist and may cause bearing and oil pump wear, as water does not make a good lubricant. Hybrid compatible engine oils must provide robust bearing performance and advanced dispersants to stop the formation of free water.
Unburnt fuel can also be problematic. Engines are at their most efficient at optimum running temperature, but colder running under a variety of loads may result in excess fuel finding its way into the sump. This can dilute the oil, affecting the integrity of the protective oil film generated, which again can cause bearing and oil pump wear. Again, as with free water, the formulation of the engine oil used must compensate for this happening.
The motor oil used in Hybrid engines has a tough life and the oil's physical and chemical properties are continually being refined to reduce the side effects of this challenging work cycle.
Selecting the Correct Engine Oil
What does this all mean for car engine oils? The main point is that the engine oil has a lot of work to do! All these advances and innovations in engine design have led to the release of the appropriate International and OEM specifications to complement and form a critical part of how the engine oils are formulated and used. Each OEM has taken slightly different approaches to achieving the common goals of improved efficiency, increased reliability, and reduced emissions. Therefore, the engine oil needs to be formulated to work with each of the OEMs chosen engine designs. Engine Oil should always be selected by following the engine/vehicle manufacturer’s requirements.
Vehicles in Warranty
Most vehicles in warranty will be serviced by the main dealer who will change the engine oil with an OEM-approved product. However, the consumer still has the power to make their own choice when it comes to engine oils. Following the departure from the European Union, the UK Government has legislated to retain the EU Block Exemption Regulation No. 461/2010. This ruling encourages and ensures freedom of choice for the consumer. In other words, an engine oil that is not formally approved, but can be supported by full documentation that it meets the vehicle’s specifications, can still be used and the OEM cannot reject a warranty claim, whatever the reason. There are only two exceptions to this: If a maintenance agreement has been signed specifying an engine oil by name, or the oil is being provided free of charge by the garage carrying out the service.
Formal OEM approval aside, the engine oil choice should still be made to ensure compliance with the manufacturer’s recommendations. Again, this will ensure maximum levels of protection, which should carry on outside of the warranty period.
Out of Warranty Vehicles
Even with older vehicles that are out of warranty, it is still important to use the correct engine oil. As these various engine technologies have been introduced, the international specifications and OEM specifications that have emerged have been added to service literature and owner’s manuals. The guidance has always been to use the type of engine oil specified by the OEM to provide the highest level of protection for that engine.
Obviously, all new cars have a manufacturer’s warranty and most cars will be returned to the main dealer for servicing. The service will be carried out as per the OEMs requirements including the use of engine oil with the correct performance level. This ensures a maximum level of protection. So why would you stop using the correct engine oil when the warranty period is over? To keep that vehicle on the road for many years after the warranty period has ended it is advisable to carry on where the main dealer left off. Best practice is to always check the handbook or get technical advice if there is any uncertainty as to which engine oil should be used.
In Summary
As we move forward, environmental legislation will continue to drive innovation, pushing engine design even further. The electric vehicle (EV) market will have its place, but with intense research going into alternative fuels, such as hydrogen, carbon neutral synthetics and biofuels, the internal combustion engine will become more advanced and, as it has always been, engine oil technology will continue to be that critical component.
If you are unsure which oil suits your needs, there is no need to worry, Morris Lubricants is here to help. You can call the Morris Lubricants Technical Helpline on 01743 237541, or use the company’s whatoil lubricant lookup feature on the website at www.morrislubricants.co.uk. Simply enter a registration number or search a wide variety of vehicles by entering the age, make and model and the ideal oil is shown.
Written by Adrian Hill, Morris Lubricants Technology Manager
Disclaimer. The above is a generalised timeline of the widespread adoption of these technologies there are exceptions that do exist.