Oils well that ends well
GAVIN MYERS and Mitch Launspach – inland sales manager: commercial, at Fuchs Lubricants South Africa – drop down to molecular level to find out how oils protect a vehicle’s vital mechanical components
Modern truck engines operate at high temperatures, generally for long periods and under heavy loads. Stress on mechanical components can be extreme and, as such, require the highest quality lubricants (as specified by the manufacturers of these components) to ensure reliability and longevity.
A modern lubricant therefore needs to perform a multitude of jobs to keep things running smoothly. The lubricants you use in your major driveline components (engine, gearbox and differentials) need to be of high quality. But what does that mean?
The importance of quality
Most locally manufactured lubricants will carry a European Automotive Manufacturers Association (ACEA) specification and an American Petroleum Institute (API) specification.
“The best lubricant recommendations are those of the manufacturers themselves. Engineers spend years designing and developing each specific piece of equipment. They know the exact lubrication and additive mix requirements and the quantity of additive pack to be used (treat rate) for the equipment to operate at peak levels under the most extreme conditions,” says Launspach.
All this leads us to two important questions. What are the main functions of oil? Which one is best to use?
Oils are available in mineral, semi-synthetic or fully synthetic forms, each with different properties brought about by the number of different refining processes.
“Each additional process creates a more stable, homogeneous and higher-quality base oil. After the initial refining process (which is purely a distillation process) the resulting base oil is called a Group I mineral oil, and is suitable for the manufacture of a wide range of automotive and industrial lubricants.
“A second process will produce a base oil of a slightly higher quality, which is now a Group II mineral base oil.
“Following a third refining process, the oil would be classed as a Group III base oil and is now also classed as a semi-synthetic base oil.
“Further refining creates Group IV poly-alphaolefin base oils, and Group V Poly Alkaline Glycol and Ester base oils,” Launspach explains.
Both Group IV and Group V are considered full-synthetic base oils, and are used in the manufacture of the highest-quality lubricants.
“The various categories are directly related to quality, but are in no way related to the viscosity (thickness) of the oil. In all critical performance parameters, synthetic lubricants provide significant advantages over – and easily outperform – mineral oils,” he adds.
Oils have five main areas of function that ensure the smooth and healthy running of a vehicle.
Most high-spec engine oils are now manufactured with synthetic or semi-synthetic base oils as these are more stable under high-temperature and high-stress operations.
“It is important that the lubricant maintains a strong oil film to reduce the heat caused by friction and protect the moving parts from metal-to-metal contact, which could result in high wear levels.
“The lubricant will also absorb the heat generated by friction and carry it away from the moving parts, giving the oil sufficient time to cool and regain its optimum viscosity,” says Launspach.
A second major problem resulting from high temperatures is the fact that the oil reacts with the oxygen in the atmosphere and causes the oil to oxidise, which increases the viscosity of the oil.
Over a period of time the oxidation process accelerates, reducing effective lubrication to the moving parts and reducing energy. This process is combatted by specific additives that slow down the process of oxidation.
“Engine oils also contain additives that help them to clean the soot resulting from the combustion process, and hold it in suspension until it can be filtered out of the system. This process is called detergency and dispersency, and allows the quality and efficiency of the oil to be maintained for longer,” explains Launspach.
Special anti-corrosion additives protect the engine from corrosion caused by poor-quality, high-sulphur diesel. During the combustion process, the sulphur combines with the moisture and oxygen in the air and forms sulphuric acid.
“This acid is highly corrosive and it attacks all metal parts with which it comes into contact. The oil’s ability to combat this corrosion, which is indicated by the total base number (TBN), will be effective for a period of time,” says Launspach. He advises that fleet owners always ensure they use the best-quality diesel available, or reduce the drain intervals when operating in areas where diesel quality is poor.
4. Fuel dilution
In an engine, fuel can wash past the piston rings and contaminate the motor oil, causing it to lose viscosity. “Frequent short trips that don’t allow the oil to reach normal operating temperature can be especially problematic, because the fuel won’t volatilise and exit through the positive crankcase ventilation (PCV) system.
“Excessive fuel dilution leads to sludge and varnish, requiring the oil to be changed more often,” explains Launspach.
Very importantly, the oil is also the carrier for the many critical additives that give it the special qualities that enable it to perform as required by the engine manufacturer, with a suitable safety margin.
Can oil be re-refined?
Launspach advises against this practice. The process required to produce higher-quality base oil from a conglomeration of numerous used lubricants (which contain remnants of various additives, wear metals, water and high levels of oxidised oils) requires highly specialised equipment. While lubricants manufactured using re-refined base oils are generally cheaper, it is hard to know the precise quality of the re-refined product.
Do transmission oils differ significantly?
Many of the requirements for transmission oils are the same as for engine oils, but with less of a focus on high temperatures and protection from harmful combustion products.
“The most critical function of a transmission lubricant is to keep moving parts apart in order to reduce wear, thereby reducing the friction that results from metal to metal contact,” says Launspach.
“All of the factors mentioned above – specifically with regard to the importance of following the original equipment manufacturer’s recommendations in terms of the use of approved lubricants, including a lubricant manufactured with the specified quality base oil and observing the specified drain intervals – are vital for the protection of your transmission,” he adds.