Sulphated ASH (SAPS) – how to control too much of a good thing.

Sulphated Ash and SAPS (Sulphated Ash Phosphorus & Sulphur) (30ml)In engines the lubricant coats the liner and rings to provide a fluid film between these and the piston. The piston rings function is to separate the combustion chamber from the lube oil, but no system is perfect and small quantities of lube oil over time come into contact with combustion gases and enter the combustion chamber. Lube oil when heated will burn to form the gases carbon dioxide and water as does the fuel, but the metal additives such as Calcium, Magnesium and Zinc which are important engine oil additives will form an ash rather than a gas. This ash has two related issues.

  • It will be blown out of the exhaust and hence cause environmental pollution. These contribute to the particulates often measured when determining tax implications on cars and trucks.
  • The ash remains hot even after the compression stroke has ended and can cause pre-ignition when the piston is not at top-dead-centre.

Tested On: SAPS on Engine oils and Sulphated Ash only on greases.

Diagnostic significance: This is important when confirming the correct specification of oil has been used. Sulphated ash is important for the particulate emissions standards, but this is part of the larger SAPS standards. The Phosphorus and Sulphur are important because these are catalytic converter poisons, leading to increased exhaust emissions. LearnOilAnalysis have worked heavily with several Truck and agricultural OEMs researching this issue. Equally, the Sulphur promotes Sulphur Oxides (SOx), which form acid raid. Therefore, the SAPS standards monitor the particulate emissions (sulphated ash), and exhaust emissions (Sulphur and Phosphorus) Lubricant manufacturers in low SAPS oils use ashless additives as substitutes.

Typical Diagnostic limit  – A table of ACEA specification limits is listed below.

LearnOilAnalysis Summary of ACEA 2012 SAPS data
TestA1 / B1A3/B3A3 / B4A5 / B5C1C2C3C4E4E6E7E9
Min Base Number (mg KOH/g)8108612797
Max Sulphur (ppm)200030003000200030004000
Phosphorus (ppm)≤500≤900

≥ 700 &

≤ 900

Sulphated ash (%)≤1.3≥ 0.9 & ≤1.5≥ 1.0 & ≤1.6 ≤ 1.6≤ 0.5≤ 0.8≤ 0.52121