Extreme-pressure additives — primarily sulphurised olefin, sulphurised fatty ester and phosphate ester — form sacrificial sulphide / phosphide films on steel under shock loading, preventing scuffing, scoring and welding in heavily-loaded gear meshes, hypoid axles and heavy-duty manual transmissions. This guide covers EP chemistry families, treat rates for API GL-4 / GL-5 / MT-1 / SAE J2360, Timken / Four-Ball / FZG test methods, regulatory shift away from chlorinated paraffin, and Indian sourcing.
| Service Spec | EP Treat % (finished) | Active S % | P (ppm) | Timken OK Target (lbf) |
|---|---|---|---|---|
| API GL-4 (manual trans, transaxle) | 4-5% | 2-3% | 800-1200 | 40-50 |
| API GL-5 (hypoid rear axle) | 5-7% | 3-5% | 1500-2000 | 60+ |
| API GL-5 LS (limited-slip) | 5-7% + FM | 3-5% | 1500-2000 | 60+ |
| API MT-1 (HD manual trans) | 4-5% + syncro-FM | 2-3% | 1000-1500 | 45-55 |
| SAE J2360 (OEM gear oil) | 5-7% | 3-5% | 1500-2000 | 60+ |
| ATF Dexron / Mercon | 1-2% (P-ester) | <0.5% | 800-1200 | 25-35 |
| Test | Method | What it Measures | GL-5 Target |
|---|---|---|---|
| Timken OK Load | ASTM D2782 | Max load that EP film supports without scoring | 60+ lbf |
| Four-Ball Weld Load | ASTM D2783 | Load at which microweld occurs between 3 balls + 1 | 300+ kgf |
| FZG Fail Stage | DIN ISO 14635 / ASTM D5182 | Gear-tooth scuffing load stage (1-12) | Stage 12+ |
| L-37 Axle Test | ASTM D5704 | Hypoid axle protection at low speed / high torque | Pass GM Stamping |
| L-60-1 Thermal Stability | ASTM D5662 | Gear oil thermal-oxidative stability | Pass GM |
| IS 1448 P-110 EP | BIS Indian Std | Indian gear oil EP test panel | Pass IS-GL-5 |
API GL-4 (manual transmission, transaxle, mild-condition hypoid gear) uses 4-5% EP additive in finished oil with active sulphur 2-3% — corresponds to Timken OK Load 40-50 lbf, Four-Ball Weld 200-250 kgf. API GL-5 (hypoid rear axle, severe-condition gear) uses 5-7% EP with active S 3-5% — Timken OK 60+ lbf, Four-Ball Weld 300+ kgf.
API GL-5 LS (limited-slip differential) uses similar EP plus friction modifier. API MT-1 (heavy-duty manual transmission) uses GL-4-level EP plus syncro-friction-friendly chemistry.
Under shock loading (gear tooth meshing, axle loaded under torque), instantaneous flash temperature at the contact reaches 600-1000 °C — high enough to thermally decompose the EP additive at the contact. Sulphurised olefin decomposes to release active sulphur that reacts with steel to form FeS (iron sulphide) sacrificial film — softer than steel, scuffs preferentially, prevents micro-welding.
Phosphate ester decomposes to release phosphorus that forms FeP/Fe3P phosphide film. Sulphur-phosphorus together gives synergistic film with both anti-scuffing (S) and anti-wear (P) action.
For NSF H1 / H2 food-grade gear oil and incidental-food-contact lubricants, regulatory restrictions prohibit traditional sulphurised olefin and chlorinated paraffin. Sulphurised fatty ester (sulphurised lard oil substitutes — rapeseed methyl ester + S2Cl2 derivatives, or sulphurised TMP-trioleate) gives EP function with food-grade-acceptable chemistry.
Treat rate 5-9% for H1-class gear oil. Performance is slightly below sulphurised olefin — Timken OK ~40-50 lbf vs 60+ lbf — but adequate for most food-machine gear applications.
Short-chain chlorinated paraffin (SCCP, C10-C13) is restricted under the Stockholm Convention as a persistent organic pollutant. Medium-chain (MCCP, C14-C17) is under regulatory review in EU and increasingly restricted. Long-chain (LCCP, C18-C30) is currently unrestricted but under scrutiny.
Lubricant blenders selling into EU OEMs are required to use MCCP or LCCP — or move entirely away from chlorinated chemistry. SCCP is essentially out of new formulations globally. Sulphurised olefin + phosphate ester combination replaces chlorinated EP without performance loss in most applications.
Both test EP but measure different aspects. Timken OK Load (ASTM D2782) measures the maximum load that the EP film can support without scoring — a single-point steady-load test. API GL-5 target Timken OK 60+ lbf. Four-Ball Weld Load (ASTM D2783) measures the load that causes microweld between three stationary balls and one rotating ball under increasing load. API GL-5 target 300+ kgf.
Timken correlates better to hypoid axle scoring; Four-Ball correlates better to gear tooth scuffing. Most EP specifications require both tests.
Branded EP from Lubrizol Anglamol 99 / 6080, Afton HiTEC 343 / 1530 / 1540, Infineum C9425 EP, BRB International (Belgium) sulphurised products, Chemtura/LANXESS Vanlube. India landed ₹320-460 / kg.
Lubechem custom equivalents (LC-EP-SULF-OLF sulphurised olefin, LC-EP-PHOS phosphate ester, LC-EP-GL5-01 complete gear EP package) ₹220-310 / kg — 28-35% saving. PIB feedstock and olefin sourcing from Indian distributors (BRB Mumbai, Stepan). For the full picture across chemistries, see our guide to lubricant additive suppliers in India.
API GL-5 hypoid axle EP package is sulphur-phosphorus heavy (3-5% active S, 1500-2000 ppm P) to give Timken OK 60+ for the high-load hypoid meshing geometry. The friction profile is high — fine for axle but unacceptable in manual transmission synchroniser.
API MT-1 (heavy-duty manual transmission) uses lower sulphur (2-3% active S) plus friction-modifying chemistry tuned for syncro engagement. SAE J2360 spec adds further constraints. GL-5 axle EP cannot be used directly in MT-1 transmission — separate formulation required.
For mid-volume gear oil blenders (500-5,000 MT/year), custom EP package saves ₹15-30 lakh per year on additive cost. The S-P EP chemistry route (sulphurised olefin from PIB / olefin + S, phosphate ester from alcohol + P2O5 or POCl3, plus CI/AO supporting cast) is well-established.
Lubechem builds custom LC-EP-GL5-01 with sulphurised olefin (BRB or local manufacture), phosphate ester (BASF, Albemarle), corrosion inhibitor (King Industries), antioxidant blend. Formula IP transferred at engagement closeout.
Share your target spec (GL-4 / GL-5 / GL-5 LS / MT-1 / SAE J2360), Timken / Four-Ball / FZG target and volume. We respond within one business day with an EP package plan and indicative cost.