Lubricant glossary

General educational information, not a product approval. Always confirm the current TDS, the equipment manual and the OEM requirement before ordering.

Viscosity

A measure of an oil's resistance to flow. Engine oils are graded by SAE J300; hydraulic oils by ISO VG. Viscosity changes with temperature, so both cold and operating-temperature behaviour matter.

SAE J300

The SAE standard that defines engine-oil viscosity grades such as 5W-30 and 15W-40. It includes low-temperature pumping and cranking tests and high-temperature viscosity limits. It does not define API or ACEA performance.

15W-40

A multigrade engine-oil viscosity grade. 15W describes cold-start behaviour; 40 is the high-temperature viscosity. It is not a quality class; the API or ACEA category and OEM approval are separate.

API service category

A performance classification from the American Petroleum Institute. S categories cover gasoline engines (for example SL, SN and SP); C categories cover diesel engines (for example CH-4, CI-4 and CJ-4).

ACEA

Performance sequences from the European Automobile Manufacturers' Association, covering A/B (gasoline and diesel), C (catalyst and GPF) and E (heavy-duty diesel). ACEA and API are separate systems.

OEM approval

A formal approval from a vehicle or equipment manufacturer for a specific product. It is product-specific and should be evidenced in writing; API or ACEA categories alone are not an OEM approval.

TBN

Total base number: a measure of an oil's alkaline reserve. It can help monitor depletion in service, but a higher TBN is not automatically better; the formulation and application matter.

HTHS

High-temperature high-shear viscosity, measured under conditions that resemble bearings and high-load contacts. Some OEM specifications set minimum HTHS limits.

Flash point

The temperature at which an oil's vapour can ignite under the test conditions. It is relevant to safety, volatility and storage, not a standalone performance grade.

Pour point

The lowest temperature at which the oil still flows under the test. It indicates cold-weather behaviour, but the SAE W grade and pumpability tests are separate.

Viscosity index

A number describing how much viscosity changes with temperature. A higher VI means a smaller change, but it is not a substitute for the SAE grade or OEM approval.

Base oil group

API groups I–V classify base oils by refining and composition. Group I is mineral; Groups II and III are more severely refined; Group IV is PAO; Group V covers esters and other synthetics. Finished-oil performance depends on the full formulation.

Synthetic blend

An oil containing a mixture of base oils, often mineral and synthetic. The term is not standardised across markets; check the TDS for base-oil type and approvals rather than relying on the label alone.

ATF

Automatic transmission fluid, formulated for the hydraulic, clutch and gear requirements of a conventional automatic transmission. There are many ATF specifications; a fluid is not universal.

CVT fluid

A fluid formulated for the belt or chain and pulley system of a continuously variable transmission. It has a different friction profile from ATF and must not be substituted.

ISO VG

ISO viscosity grade, defined at 40°C. Hydraulic oils are commonly described as ISO VG 46 or 68; the number is a viscosity band, not a quality ranking.

TDS

Technical data sheet: typical properties, performance claims, approvals and pack information for a specific product. Always request the current version for the exact product.

SDS

Safety data sheet: hazard, handling, storage, transport and emergency information. It is not a performance specification.

COA

Certificate of analysis: batch-specific test results. It helps confirm that the delivered batch meets the agreed specification; availability varies by supplier and product.

OEM / private label

OEM or private-label supply means the product is made or packed for a buyer's brand. It is different from an OEM approval; the commercial and technical responsibilities must be defined in writing.