What the numbers on the pack mean.
A short reference for engineers: how viscosity grades, base number and service categories are defined, and what they do not tell you. Each section names its source.
Engine oils
SAE J300 viscosity grades
A multigrade such as 15W-40 meets one cold grade and one hot grade at the same time.
The W grades are set by a maximum cranking viscosity and a maximum pumping viscosity at low temperature. The hot grades are set by kinematic viscosity at 100 °C, plus a minimum high-temperature, high-shear viscosity at 150 °C.
| Grade | Side | Limit |
|---|---|---|
| 5W | Cold | Cranking ≤ 6,600 mPa·s at −30 °C; pumping ≤ 60,000 mPa·s at −35 °C |
| 10W | Cold | Cranking ≤ 7,000 mPa·s at −25 °C; pumping ≤ 60,000 mPa·s at −30 °C |
| 15W | Cold | Cranking ≤ 7,000 mPa·s at −20 °C; pumping ≤ 60,000 mPa·s at −25 °C |
| 30 | Hot | 9.3 to < 12.5 mm²/s at 100 °C; HTHS ≥ 2.9 mPa·s |
| 40 | Hot | 12.5 to < 16.3 mm²/s at 100 °C; HTHS ≥ 3.7 mPa·s for 15W-40 |
SAE engine-oil grades and SAE gear-oil grades (J306, such as 80W-90) are separate scales with no relationship between them.
Hydraulic, compressor and turbine oils
ISO VG
ISO 3448 grades industrial oils by kinematic viscosity at 40 °C.
The number is the mid-point of the band in mm²/s, and each band runs 10 % either side. ISO VG says nothing about performance: whether a fluid is anti-wear (HM), high viscosity index (HV), a compressor oil (L-DAJ) or a turbine oil (L-TSA) is a separate classification.
| Grade | KV at 40 °C | Stocked example |
|---|---|---|
| VG 32 | 28.8–35.2 mm²/s | Tellus S2 MX 32 |
| VG 46 | 41.4–50.6 mm²/s | Turbo T 46 |
| VG 68 | 61.2–74.8 mm²/s | Tellus S2 VX 68, Corena S4 R 68 |
Marine diesels
Base number (BN or TBN)
The oil's alkaline reserve, in mg KOH/g, measured by ASTM D2896.
Crankcase oils in trunk-piston engines must neutralise combustion acids from sulphur in the fuel, so Shell scales base number to fuel sulphur across its medium-speed range. Tracking BN in service shows how quickly the additive reserve is being used.
| Shell oil | BN | Fuel |
|---|---|---|
| Gadinia S3 | 12 | Distillate, up to 1 % sulphur |
| Argina S2 | 20 | Up to 0.5 % sulphur |
| Argina S3 | 30 | Residual, up to 3 % sulphur |
| Argina S4 | 40 | Above 2 % sulphur |
| Argina S5 | 55 | Above 3 % sulphur |
Service categories
API categories
C categories are for diesel engines, S categories for petrol engines.
| Category | Status | Notes |
|---|---|---|
| CK-4 | Current | For 2017 on-highway and Tier 4 engines; backward compatible with CJ-4, CI-4 Plus, CI-4 and CH-4 |
| FA-4 | Current | XW-30 only, for selected 2017+ engines; not backward compatible |
| CJ-4, CI-4, CH-4 | Current | For 2010, 2002/2004 and 1998 engines |
| CF, CF-2 | Obsolete | Not suitable for most diesel engines built after 2009 |
| SP | Current | Petrol engines; adds low-speed pre-ignition and timing-chain wear protection |
| SN | Current | For 2020 and older petrol engines |
What the oil is made from
Base-oil groups
API sorts base stocks into five groups by saturates, sulphur and viscosity index.
| Group | Definition | Stocked examples |
|---|---|---|
| I | < 90 % saturates and/or > 0.03 % sulphur; VI 80–120 | — |
| II | ≥ 90 % saturates, ≤ 0.03 % sulphur; VI 80–120 | Rimula R4 L, Tellus S2 MX and VX |
| III | ≥ 90 % saturates, ≤ 0.03 % sulphur; VI ≥ 120 | — |
| IV | Polyalphaolefins (PAO) | Corena S4 R 68 |
| V | All other base stocks, such as esters | — |
Helix Ultra uses Shell PurePlus, a synthetic base oil made from natural gas (gas-to-liquids).
Outboards
NMMA TC-W3
The standard for two-stroke, water-cooled marine engine oils.
TC-W3 is a performance standard owned by the National Marine Manufacturers Association. Certification combines bench tests (fluidity, miscibility, rust, compatibility) with running-engine tests that assess ring sticking and piston deposits. Certified oils carry an RL number you can check on NMMA's register; Nautilus Premium Outboard is registered as RL-00444K.
TC-W3 is for two-stroke outboards only. Four-stroke outboards need a four-stroke oil.
Machinery
Why compressor oil is not engine oil
The two are built for different jobs.
Rotary compressor oils such as Corena S4 R run for thousands of hours above 100 °C discharge temperature. Shell formulates them for low deposit formation on rotors and separators, low volatility to limit carry-over into the air, fast air release, water separation and an ashless anti-wear system. Diesel engine oils carry detergents and a base-number reserve to neutralise combustion acids, with sulphated ash of around 1–1.5 %.
The compressor maker's manual sets the oil, not the engine-oil grade. Shell notes that diluting Corena S4 R with mineral oil markedly reduces its performance.
Sources