Viscosity / HTHS rate viscosity
Viscosity describes the internal friction of fluids and indicates their flow characteristics at low and high temperatures.
High Temperature High Shear (HTHS) rate viscosity – indicates dynamic viscosity and is measured in millipascal seconds (mPa*s) at 150 °C and under extremely high shear loads of up to 106 s-1. It describes the characteristics of lubricants under certain operating conditions at the cylinder wall or inside the connecting rod or crankshaft bearing.
Low HTHS: 2.9 – 3.5 mPas = low HTHS viscosity, allows for low fuel consumption. High HTHS: > 3.5 mPas = high HTHS viscosity, high degree of wear protection.
SAE viscosity grades
The viscosity grades of engine oils are defined by the SAE J300 (Society oft Automotive Engineers), for instance SAE 10W40: The number preceding the letter W indicates the viscosity at low temperatures; the smaller the value in front of the W, the lower the viscosity of the oil at low temperatures. (the “W” stands for winter). The number following the W represents the viscosity at high temperatures; the higher the warm viscosity, the higher the loads the oil can handle at high temperatures. To avoid any confusion between engine and transmission oils, the viscosity grades applying to transmission oils are defined following SAE J306 (e.g. SAE 75W90).
Temperature ranges for motor oils
The SAPS level defines the portion of sulfate ash, phosphorus, and sulfur in engine oils.
Low SAPS – strictly limited portion of sulfate ash (< 0.5 %), phosphorus (0.05 %), and sulfur (< 0.2 %). Mid SAPS – limited portion of sulfate ash (< 0.8 %), phosphorus (0.07 – 0.09 %), and sulfur (< 0.3 %). Full SAPS – no limitations to the portion of sulfate ash, phosphorus, and sulfur.
The classifications of the API (American Petroleum Institute) describe the quality requirements to be met by engine and transmission oil in the United States.
As the operating conditions and engine characteristics fundamentally differ between Europe and the United States, the ACEA (Association des Constructeurs Européens d’Automobiles) introduced its own classification system in 1996. While based on the API classifications, the ACEA sequences focus to a greater extent on the specific lubricant requirements that apply to engines built into European automobiles as well as the respective EURO emission standards. Meeting these requirements also involves the successful completion of test runs for lubricants used in European test engines. The current ACES sequences are grouped into A sequences (A1, A3, and A5) for passenger car gas engines, B sequences (B1, B3, B4, and B5) for engine oils used in diesel passenger cars, C sequences (C1, C2, C3, and C4) for engine oils with a limited SAPS level, and E sequences (E2, E4, E6, E7, and E9) for engine oils used in diesel trucks.
Fuel-economy engine oils
Fuel-economy engine oils are defined as oils that allow for a low consumption of fuel.