Gear oil is defined by its extreme-pressure (EP) capability — the sulphur-phosphorus chemistry that forms a sacrificial chemical film at gear tooth contact under load. Automotive gear oil follows the API GL hierarchy (GL-1 through GL-5 plus MT-1) and the SAE J306 viscosity grades (75W-90, 80W-90, 85W-140). Industrial gear oil follows DIN 51517-3 CLP across ISO VG 68 through 680, used in cement, sugar, paper, mining and heavy industrial gearboxes. ATF, CVT and DCT are separate fluid families that share gear oil's heritage but with quite different chemistry. This guide covers the EP chemistry, viscosity grade selection, yellow-metal compatibility and the practical Indian formulation choices.
| Component | Function | Typical % (m/m) | Notes |
|---|---|---|---|
| Base oil — Group I SN500 | Bulk viscosity | 55–65% | Group I workhorse for 80W-90 GL-5 |
| Base oil — Group I BS150 | High-viscosity contribution | 20–30% | Bright stock for 80W-90 viscosity build |
| Sulphurised olefin EP additive | Active sulphur for EP film | 3–5% | 10–15% S in additive; delivers 1.8–2.2% S in finished |
| Dialkyl dithiophosphate / phosphate ester | Phosphorus contribution; antiwear | 0.5–1.2% | Synergy with sulphurised olefin |
| Amine borate (yellow metal protector) | Suppresses Cu / brass attack | 0.3–0.8% | Critical for GL-5 yellow-metal compatibility |
| Aminic antioxidant (ADPA) | Oxidation stability at high temp | 0.2–0.5% | Important for D5704 thermal stability |
| Friction modifier (MoDTC or organic) | Reduces friction at gear contact | 0.1–0.3% | Optional; improves efficiency |
| Polyisobutylene (tackifier) | Adhesion to gear teeth, leakage prevention | 0.5–1.5% | Used in many GL-5 formulations |
| Demulsifier | Water shedding | 30–100 ppm | Less critical than hydraulic but specified |
| PMA pour point depressant | Cold-pumping at −26 °C | 0.1–0.3% | For 80W specification |
| Silicone defoamer | Foam suppression | 5–20 ppm | Standard treat |
A finished 80W-90 GL-5 carries 1.8–2.2% active sulphur and 0.08–0.12% phosphorus — the sulphur level is the practical distinguisher between GL-4 and GL-5. The complete EP package is typically purchased as a commercial concentrate from Lubrizol, Infineum, Chevron Oronite or Afton, dosed at 5–8% in finished oil. Component-by-component blending is possible for very large producers but rarely justifies the QC overhead at Indian production scale.
| SAE Grade | Brookfield 150 kPas Max At | KV at 100 °C (cSt) | Typical Indian Application |
|---|---|---|---|
| 75W | −40 °C | 4.1 min | Premium 75W-90 synthetic |
| 80W | −26 °C | 7.0 min | 80W-90 workhorse manual / axle |
| 85W | −12 °C | 11.0 min | 85W-140 heavy duty axle |
| 90 | n/a (monograde high) | 13.5–18.5 | Multigrade upper boundary & monograde |
| 140 | n/a | 24.0–32.5 | Heavy-duty hot-climate axle |
| 250 | n/a | ≥41.0 | Heavy industrial & off-highway extreme |
80W-90 multigrade is the dominant gear oil grade in India by far — it covers most passenger and light commercial gearboxes and most differentials in moderate climates. 85W-140 is preferred for heavy commercial trucks in hot climates where sustained oil temperature in the diff can exceed 110 °C. 75W-90 is the premium synthetic / semi-synthetic grade for modern passenger SUVs and is a growing aftermarket segment.
Industrial gear oil for cement mills, sugar mills, paper machines, mining gearboxes, marine reduction gear, wind turbine gearboxes and the like is specified under DIN 51517-3 CLP (Closed circuit, Lubricants, Pressure) at ISO VG 68, 100, 150, 220, 320, 460 and 680. The chemistry is similar to automotive GL-5 in EP approach but tuned for very long drain life (5,000–15,000 hours) and continuous high-load operation rather than the intermittent shock-load profile of automotive.
| Property | Test Method | CLP 220 Limit | Design Target |
|---|---|---|---|
| KV at 40 °C | D445 | 198–242 cSt | 215–230 |
| KV at 100 °C | D445 | Report | 18–20 cSt |
| Viscosity Index | D2270 | ≥90 | 95–110 |
| Pour point | D97 | ≤−9 °C | −15 to −21 |
| Flash point | D92 | ≥200 °C | 230–250 |
| Demulsibility @ 82 °C | D1401 | 40/40/0 in 30 min | In 15–20 min |
| FZG load stage | A/8.3/90 | ≥12 | 13–14 |
| Foam Seq I / II / III | D892 | 100/0, 50/0, 100/0 ml | <30 / 0 |
| Copper corrosion | D130 | 1 max | 1a |
| Rust D665A/B | D665 | Pass | Pass |
| Oxidation (CKD test) | DIN 51354 | ≥500 hr | 800–1,500 |
| Micro-pitting (FVA 54) | FVA-54 | ≥10 GFT | 10–Higher |
API GL-4 is a moderate-EP gear oil for manual gearboxes and spiral-bevel differentials. API GL-5 is a high-EP gear oil for hypoid differentials with high sliding contact (typical for trucks, SUVs, pickup trucks). The difference is the active sulphur content of the EP additive — GL-4 typically 1.0–1.5% S, GL-5 typically 1.8–2.5% S.
GL-5 EP additive is more corrosive to yellow metals (brass, bronze) — which is why GL-5 should not be used in synchromesh gearboxes that have brass synchronisers.
Sulphur-phosphorus (S-P) chemistry is the workhorse. The EP package contains sulphurised olefins (active sulphur source), dialkyl phosphites or phosphate esters (phosphorus source), and amine-borate or alkyl thiocarbamate as a friction modifier and yellow-metal protector. Typical S:P ratio is 4:1 to 6:1 by weight. Total EP package treat rate is 4–8% in finished GL-5 gear oil.
Automotive gear oil grades follow SAE J306: 80W-90 is the workhorse for medium-duty manual gearboxes and light-truck differentials (KV100 13.5–18.5 cSt). 85W-140 is preferred for heavy-duty truck and tractor differentials in hot climates (KV100 24–32.5 cSt). 75W-90 is a synthetic / semi-synthetic premium grade for modern passenger SUVs.
For industrial CLP gear oils, ISO VG 68 / 100 / 150 / 220 / 320 / 460 / 680 are the standard grades per DIN 51517-3.
No — generally not. Most manual gearboxes use brass synchronisers, and the higher active-sulphur content of GL-5 EP additive will attack the brass over time, causing synchroniser failure. Manual gearboxes specify GL-4 or, in some cases, a specific 'GL-4+' formulation. Hypoid differentials (rear axles) require GL-5.
The recent MT-1 / API MT-1 specification adds heavy-duty manual transmission requirements on top of GL-5 — for combined gearbox-axle units in heavy trucks.
BIS IS 1118 (most recent revision) is the Indian Standard for automotive gear oil — covering EP gear oils for manual transmissions and axle differentials. It is closely aligned with API GL-4 and GL-5 categorisation, with property limits on KV40, KV100, VI, flash, pour, foam, copper corrosion and EP performance via four-ball weld load. BIS IS 1118 certification is required for branded gear oil supplied to the Indian aftermarket through the ISI mark — see our compliance service for BIS support.
Automatic Transmission Fluid (ATF) is a separate category — used in planetary automatic transmissions. It has much lower viscosity (~7 cSt at 100 °C), is dyed red, contains friction modifiers tuned for clutch and band engagement, and has no EP additive. CVT fluid uses friction modifiers tuned for belt/pulley grip. DCT fluid is closer to ATF but tuned for the wet-clutch friction profile of dual-clutch transmissions.
Each is OEM-specific (Toyota WS, GM Dexron, Ford Mercon, Honda CVT, Hyundai SP, etc.) and cannot be cross-substituted.
ASTM D5704 (the Mack T-12 / CRC L-60-1) is a thermal and oxidative stability test for axle gear oils. The test runs at 163 °C for 50 hours with air bubbling, then measures viscosity increase, insolubles, and visible deposit on a test plate. It is the primary qualification for MT-1 and GL-5 Plus claims for heavy-duty truck axles. ASTM D7038 (L-37) is the related axle gear test under load.
Polyisobutylene (PIB) tackifier is added at 0.5–1.5% to improve adhesion of the oil to gear teeth, reduce leakage from imperfectly sealed gear cases, and provide some stringiness for open gear applications. It is commercially valuable as a visible quality signal — consumers and workshops associate the “stringy” oil with EP performance. The viscosity contribution must be accounted for in the recipe; PIB typically adds 1.5–3 cSt at 100 °C to the finished oil.
Share your target category (GL-4 / GL-5 / MT-1 / CLP), viscosity grade (80W-90 / 85W-140 / VG 220), customer mix (manual gearbox / hypoid axle / industrial) and production scale. We respond within one business day with a formulation plan and BOM.