Low SAPS Engine Oils: Juri Sudheimer on Balancing Engine Protection and Exhaust Aftertreatment Efficiency
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Exhaust aftertreatment systems were developed to protect the environment and human health from toxic engine emissions—primarily nitrogen oxides (NOx)—and to meet increasingly stringent environmental standards that began tightening in the 1970s with the introduction of the first catalytic converters and exhaust gas recirculation systems (EGR). Their primary function is to safely reduce the concentration of, and neutralize, harmful substances such as NOx, CO, and unburned hydrocarbons before they are released into the atmosphere.
Their implementation began in the 1970s, when EGR (Exhaust Gas Recirculation) systems were introduced in the United States to reduce NOx emissions.
From the mid-1970s through the 1980s, three-way catalytic converters (TWC) became widespread in gasoline engines, converting CO, NOx, and hydrocarbons into less harmful substances.
In the 1990s–2000s, diesel aftertreatment technologies advanced significantly with the introduction of diesel particulate filters (DPF) to capture solid particles (primarily soot), as well as selective catalytic reduction (SCR) systems using reagents such as AdBlue.
Today, environmental standards (Euro 5, Euro 6) continue to tighten. Aftertreatment systems have become increasingly complex and integrated, including gasoline particulate filters (GPF), all aimed at maximizing exhaust purification and reducing environmental impact.
The Impact of Fuel and Oil Components on Aftertreatment Systems
Over time, it became clear that certain components of fuel and engine oil negatively affect exhaust aftertreatment systems. Sulfur and phosphorus can poison and deactivate catalytic surfaces, reducing the efficiency of TWC and SCR systems. Sulfated ash—primarily formed from metallic additives in engine oil—accumulates in DPFs, increases backpressure, and shortens filter lifespan, as it cannot be removed through normal regeneration.
Deposits can also form in EGR and SCR systems, although their nature differs: EGR systems typically suffer from soot-oil contamination, while SCR systems may experience both sulfur poisoning of catalysts and deposits formed from urea decomposition under unfavorable operating conditions.
These challenges led to stricter limits on sulfur content in fuels and to the development of Low SAPS oils, characterized by reduced levels of sulfated ash, phosphorus, and sulfur.
Juri Sudheimer: Why Low SAPS Oils Became Essential
 Juri Sudheimer |
According to Juri Sudheimer, founder of the MANNOL brand, the emergence of Low SAPS oils is a direct result of the evolution of exhaust aftertreatment systems. As automakers began widely implementing DPFs, GPFs, and complex multi-stage catalytic systems, it became evident that traditional additive packages could significantly reduce their service life.
Juri Sudheimer emphasizes that modern engine oils must fulfill two critical functions simultaneously: protect the engine from wear and ensure compatibility with sophisticated exhaust aftertreatment systems. This dual requirement has made the development of Low SAPS oils a key focus for lubricant manufacturers over the past two decades.
What Is Sulfated Ash and Why It Matters
Sulfated ash is the amount of inorganic residue remaining after oil is burned at high temperatures. It is measured as a percentage of the oil’s mass. This residue mainly originates from metallic additives such as calcium, magnesium, sodium, barium, zinc, potassium, and others.
In simplified terms, oil is burned to leave a residue consisting of ash and carbon compounds. The residue is then treated with sulfuric acid and reheated to approximately 775°C to oxidize the carbon. After repeated treatment and heating cycles, the remaining residue is weighed to determine the sulfated ash content.
Sulfated ash is a key parameter of fresh oil, and most modern standards impose limits on it. High ash content negatively affects particulate filters (DPF and GPF) by promoting ash accumulation. It can also impair modern multi-stage catalytic converters.
At moderate levels, however, sulfated ash is relatively harmless if the oil meets the manufacturer’s specifications. Extremely low ash levels are not always desirable either, since ash largely originates from detergent additives that help prevent deposits. Anti-wear additives such as ZDDP are also sources of ash. This creates a fundamental trade-off: too much ash is harmful, but too little can compromise engine protection.
Juri Sudheimer: Ash Content as a Balance Between Protection and Ecology
Juri Sudheimer highlights that finding the right balance is one of the most complex challenges in modern lubricant formulation. Metal-based detergents are essential for maintaining engine cleanliness, yet they also produce ash residues that can accumulate in filters and catalysts.
As a result, formulators must continuously optimize the relationship between additive performance, ash content, and environmental requirements. Modern Low SAPS oils are therefore sophisticated blends of base oils and additives designed to protect engines, improve fuel efficiency, and extend the service life of exhaust aftertreatment systems.
API Requirements for Low SAPS Oils
The American Petroleum Institute (API) defines the following requirements:
API SP:
• Phosphorus (P): 0.06–0.08% by mass (minimum 0.06% for some viscosity grades)
• Sulfur (S): max 0.5–0.6% depending on viscosity grade
• Sulfated ash (SA): not specified
API SP RC / ILSAC GF-6:
• Phosphorus: 0.06–0.08%
• Sulfur: max 0.5–0.6%
• Sulfated ash: not specified
API SQ (introduced March 2025):
• Phosphorus: 0.06–0.08%
• Sulfur: max 0.5–0.6%
• Sulfated ash: not specified
API SQ RC / ILSAC GF-7:
• Phosphorus: 0.06–0.08%
• Sulfur: max 0.5–0.6%
• Sulfated ash: max 0.9% (except 0W-8 and 0W-12 oils)
European ACEA Classification for Low SAPS Oils
In the ACEA system, oil specifications consist of a letter and a number (e.g., C3, E9). The letter indicates the oil type, while the number defines its category. Low SAPS oils for passenger cars fall under the “C” categories: C2, C3, C4, C5, C6, and C7.
They can be divided into two groups:
• High HTHS (higher viscosity under stress): C3, C4
• Fuel-efficient, low HTHS: C2, C5, C6, C7
C4 has the lowest SAPS levels and is used in engines with strict environmental requirements, particularly Renault models requiring RN0720 approval:
• Sulfated ash: ≤0.5%
• Sulfur: ≤0.2%
• Phosphorus: ≤0.09%
Other categories typically specify:
• Sulfated ash: ≤0.8%
• Sulfur: ≤0.3%
• Phosphorus: 0.07–0.09%
C2: Low-viscosity oils (e.g., 0W-30, 5W-30) for brands like PSA, Renault-Nissan, Fiat, and others. Focus on fuel economy and emissions system protection under moderate loads.
C3: Oils for vehicles requiring approvals such as VW 504 00/507 00, BMW Longlife-04, MB 229.51, Porsche C30—offering strong oil film and wear protection.
C5: Low-viscosity, fuel-efficient oils (0W-20, 5W-20) for modern vehicles, including VAG, Porsche, Mercedes-Benz, and some Chinese brands.
C6: Designed for the latest turbocharged, direct-injection engines, providing fuel efficiency, LSPI protection, and compatibility with advanced aftertreatment systems.
C7: Introduced in 2023, based on C6 performance but requiring further formulation optimization.
Erik Sudheimer: New ACEA Categories Reflect Engine Evolution
 Erik Sudheimer |
According to Erik Sudheimer, Development Director at Mannol, new ACEA categories reflect major changes in engine design. Turbocharging, direct injection, downsizing, and increased power density demand new approaches to oil formulation.
Standards like ACEA C6 and C7 not only address environmental requirements but also aim to improve fuel efficiency without compromising engine durability, often requiring lower viscosity oils and advanced additive technologies.
Low SAPS Oils as a Key Element of Modern Engine Ecology
The evolution of engine oils is closely tied to advancements in automotive technology and stricter environmental regulations. As exhaust aftertreatment systems become more sophisticated, lubricant requirements grow more demanding.
Low SAPS oils have become a critical technological solution, enabling effective engine protection while maintaining the efficiency of particulate filters and catalytic converters, reducing fuel consumption, and lowering CO₂ emissions.
As engines continue to evolve and environmental standards become stricter, the importance of these oils will only increase. Lubricant manufacturers continue to refine formulations to achieve the optimal balance between engine protection, fuel efficiency, and environmental performance.