API, ACEA and JASO specifications explained

Three bodies write the categories that matter in this market. API, the American Petroleum Institute, publishes service categories: S-series for petrol engines, C-series for compression-ignition, meaning diesel. ACEA, the European automobile manufacturers' association, publishes sequences that are generally more demanding on oxidation and deposit control. ILSAC focuses on fuel economy and emissions-system protection for petrol engines, and JASO writes the friction specifications that motorcycle wet clutches depend on.

A single oil can meet several at once. That is not marketing padding — it means the formulation passed each body's test programme.

API petrol categories run alphabetically and are backward compatible: API SP supersedes SN, SM, SL and everything before it, so an SP oil is safe where an older category was specified.

The jump worth understanding is SP. It added protection against low-speed pre-ignition, a destructive combustion event that affects small turbocharged direct-injection engines — exactly the engines that have become common in newer cars. If a vehicle has a small turbo petrol engine, SP is not optional marketing.

API CK-4 is the current heavy-duty category. Against the older CI-4 and CJ-4 it improves oxidation stability, shear stability and aeration control, and it limits sulphated ash, phosphorus and sulphur to protect diesel particulate filters and catalysts.

CK-4 is backward compatible with CJ-4, CI-4 and CH-4. CI-4 remains entirely valid for the large installed base of older engines without aftertreatment, and where fuel sulphur is high it is often run on a shortened drain interval. What you cannot do is put CI-4 into a modern engine with a particulate filter and expect the filter to survive.

ACEA A3/B4 covers high-performance petrol and light-duty diesel engines including direct injection. It is a stay-in-grade specification, which means the oil must not shear out of its viscosity band during the test.

ILSAC GF-6A is about fuel economy and emissions hardware. It caps phosphorus to protect catalytic converters and adds a timing chain wear test that earlier categories did not have.

JASO MA2 is a friction specification, not a quality one. A motorcycle shares its oil between engine, gearbox and wet clutch. Car oils contain friction modifiers that make a wet clutch slip, so a four-stroke motorcycle needs MA2 and a car oil must never be substituted.

API GL-5 describes hypoid gear oil performance under high-speed shock load. Its sulphur-phosphorus chemistry can attack yellow metals, so where a synchromesh gearbox specifies GL-4, a GL-5 is not a safe upgrade.

DIN 51524 Part 2 (HLP) is the mineral hydraulic fluid classification with anti-wear, anti-oxidation and anti-corrosion additives — the standard ask for mobile and industrial hydraulics. NLGI numbers on grease are a consistency scale, not a quality scale: NLGI 2 for most centralised systems, NLGI 3 for open bearings.