Viscosity is a key parameter of oils and lubricants, directly determining their flow properties and their ability to protect components under specific operating conditions. In engineering practice, two primary viscosity classification systems are used, each assigned to different areas of application: ISO VG and SAE.
SAE viscosity classification
The SAE classification is a system established by the Society of Automotive Engineers (SAE) to classify lubricants according to their viscosity.
SAE designations allow the oil to be matched to specific design, operational and temperature requirements of the engine. It should be noted that these parameters relate solely to viscosity and do not constitute a direct measure of oil quality.
Key parameters:
- Kinematic viscosity at 100°C – corresponds to the average viscosity of the oil during normal operation of a car engine,
- HTHS dynamic viscosity at 150°C – characterises the oil’s viscosity under extremely high thermal loads during engine operation,
- CCS dynamic viscosity at sub-zero temperatures – measures the oil’s ability to function effectively during engine start-up,
- Pumpability limit temperature – defines the extreme conditions under which the oil’s viscosity allows for engine start-up.
SAE J300 classification
The viscosity grade according to SAE J300 is a key criterion indicating the suitability of the lubricating oil for use in an engine. SAE defines six so-called winter grades (designated by the letter “W”) and nine so-called summer grades.
Winter grades (e.g. 0W, 5W, 10W) indicate viscosity at low temperatures (cold engine start-up) and the pumpability limit temperature. The lower the number before the “W”, the more fluid the oil is at sub-zero temperatures.
Summer grades (e.g. 30, 40, 50) specify kinematic viscosity at operating temperature, as well as high-temperature dynamic viscosity (HTHS). The higher the number, the thicker and more durable the oil film at high temperatures.
SAE J300 requirements: table compiled based on: Lube-Tech-113-The-Impact-of-SAE-Critical-Specifications-to-the-formulating-and-manufacture-of-automotive-oils.pdf
| SAE class | CCS dynamic viscosity (start-up) [mPa·s] | CCS test temperature [°C] | Max. pumpability (MRV) [°C] | Kinematic viscosity at 100∘C [mm²/s] |
| 0W | max 6200 | -35 | -40 | min. 3.8 |
| 5W | max 6600 | -30 | -35 | min. 3.8 |
| 10W | max 7000 | -25 | -30 | min. 4.1 |
| 15W | max 7000 | -20 | -25 | min. 5.6 |
| 20W | max 9500 | -15 | -20 | min. 5.6 |
| 8 | – | – | – | 4.0 – < 6.1 |
| 16 | – | – | – | 6.1 – < 8.2 |
| 20 | – | – | – | 6.9 – < 9.3 |
| 30 | – | – | – | 9.3 – < 12.5 |
| 40 | – | – | – | 12.5 – < 16.3 |
| 50 | – | – | – | 16.3 – < 21.9 |
SAE J306 classification
For lubricants intended for use in gearboxes, axles and mechanisms, the viscosity classification is defined by the SAE J306 standard.
It specifies the fluidity of the oil at extremely low temperatures and the strength of the lubricating film at operating temperature (100°C). It uses higher grade numbers than engine oils (e.g. 75W, 80W, 90, 140) to prevent the mistaken use of an unsuitable lubricant.
SAE J306 requirements: developed based on: Lubrication Fundamentals
| SAE Grade | Maximum temperature for viscosity 150,000 cP [°C] | Kinematic viscosity at 100∘C [mm²/s] (Min) | Kinematic viscosity at 100°C [mm²/s] (Max) |
| 70W | -55 | 4.1 | – |
| 75W | -40 | 4.1 | – |
| 80W | -26 | 7.0 | – |
| 85W | -12 | 11.0 | – |
| 80 | – | 7.0 | < 11.0 |
| 85 | – | 11.0 | < 13.5 |
| 90 | – | 13.5 | < 18.5 |
| 110 | – | 18.5 | < 24.0 |
| 140 | – | 24.0 | < 32.5 |
| 250 | – | 41.0 | – |
ISO 3448 classification – standard for industrial oils
The ISO 3448 standard (and the related ISO VG) is an international standard specifying the kinematic viscosity of industrial oils at 40°C. It defines 18 viscosity grades for industrial oils.
The key reference point for this standard is a temperature of 40°C, which corresponds to typical operating conditions for industrial machinery. The number assigned to a specific grade (e.g. ISO VG 46) indicates the average kinematic viscosity. In practice, a deviation in the viscosity of a given oil of up to ±10% from the nominal value is permitted.
The system is designed so that each successive grade has a viscosity approximately 50% higher than the previous one, allowing engineers to precisely select a lubricant to meet specific technical requirements.
The PCC Group’s offering
As a leading manufacturer of synthetic base oils and ready-to-use formulations, the PCC Group offers a wide range of products tailored to various industrial sectors.
The company supplies lubricant manufacturers with high-quality polyalkylene glycols (PAG) – synthetics characterised by significantly higher thermal stability and operational purity compared to traditional mineral oils:
- Rokolub P-B, PO-D, 50-B, 60-D series: e.g. Rokolub P-B-46 (ISO VG 46) or Rokolub 60-D-220 (ISO VG 220),
- Rokolub MOS series: e.g. Rokolub MOS 32 (ISO VG 32).
The PCC Group also supplies advanced, ready-to-use products corresponding to specific ISO VG grades:
- Flame-retardant HFDR hydraulic fluids – Rokolub FR T series (e.g. Rokolub FR T-46 ultra – ISO VG:46),
- Flame-retardant HFDU hydraulic fluids – Rokolub HYD series (e.g. Rokolub HYD 46 – ISO VG:46),
- Synthetic gear oils – Rokolub IGO WS series (e.g. Rokolub IGO WS 220 – ISO VG:220),
- Synthetic compressor oils – Rokolub 320F (ISO VG: 320).
- Lube-Tech-113-The-Impact-of-SAE-Critical-Specifications-to-the-formulating-and-manufacture-of-automotive-oils.pdf
- https://www.stle.org/files/TLTArchives/2024/07_July/Lubrication_Fundamentals.aspx
