Oils, lubes & additives 38 Beyond viscosity: Why oil specifications matter more than ever As today’s engines become ever more complex and precisely engineered, the days of choosing an oil based simply on its viscosity grade are long behind us. With this in mind, Alan Outhwaite, Head of the Verification of Lubricant Specifications (VLS) Technical Review Panel, discusses why specifications are so important when selecting engine oils for customer vehicles. Choosing the right oil really does matter. Modern vehicle engines require sophisticated lubricants using advanced chemistry. Even the slightest change in the formulation has the potential to reduce performance in the short term and cause engine damage over the long term. Some leading oil manufacturers have over 15 different SAE 5W-30 engine oils available, and it is for good reason. These oils might all be the same viscosity grade, but there are some significant differences between them that really matter. Viscosity measures only resistance to flow and tells you nothing about the oil’s performance characteristics. Some will be High SAPS (Sulphated Ash, Phosphorous and Sulphur), suitable for engines in older vehicles without exhaust after-treatment devices like catalytic converters or diesel particulate filters. Then there are mid SAPS oils for more modern vehicles with exhaust after-treatment devices, each with different OEM specification profiles; for example, ACEA C2 low High Temperature High Shear (HTHS) oils. HTHS measures the viscosity or resistance to flow of an engine lubricant at elevated temperatures under constant shear. Lower HTHS oils can improve fuel economy. However, putting a low HTHS oil in an engine not designed for it would not provide the required wear protection. Using a high SAPS oil in a low SAPS environment could negatively impact the exhaust emission system, poison the catalyst, block the diesel or gasoline particulate filters, reduce overall efficiency, and result in failure of the particulate filter or catalyst, both of which are expensive to replace. Too much phosphorus from a high SAPS oil can also poison the selective catalyst reduction units designed to control Nitrogen Oxide emissions. The latest lower viscosity 0W-16 and 0W-20 lubricants may not be suitable for many older vehicles in workshops. Backwards compatibility cannot be assumed. Subtle yet important differences concerning viscosity characteristics and/or additive chemistries are reflected in specifications that must be acknowledged during regular servicing. For example, a 2021 VW Polo 1.0 MPI requires an SAE 0W-20 engine oil complying with the latest VW 508.00 specification, part of which mandates very low HTHS properties to improve fuel efficiency. This oil would be unsuitable for a 2017 VW Polo 1.0, which requires an SAE 5W30 oil conforming to the older VW 504.00 specification, with higher and exclusively different HTHS properties. Using a VW 508.00-compliant engine oil in place of VW 504.00 could accelerate wear of engine components. In contrast, a VW 504.00-compliant engine oil instead of VW 508.00 would affect emissions and fuel economy. Specifications can be very confusing, with lubricant marketers making multiple claims for each product. Language such as ‘suitable for use’ can also be misleading, as companies do not always have technical evidence to support these claims. When deciding which product to use, we encourage technicians to use vehicle database lookup tools, check vehicle handbooks or consult their motor factor or the OEM if they are unsure. Always look beyond the viscosity to the actual specifications being claimed. Think of engine oil as another vehicle component. You wouldn’t fit a wrong air filter or brake pads. In the same way, oils are designed for each vehicle. The right specification match must be the most important decision-making factor. ukla-vls.org.uk
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