Zinc dialkyldithiophosphate (ZDDP / ZnDDP / ZnDTP) is the workhorse anti-wear additive of engine oil, industrial hydraulic oil, and many gear and grease applications. Primary alkyl, secondary alkyl, mixed primary/secondary, aryl, and ashless DTP variants give very different thermal stability and tribofilm-build characteristics. The API SP / ILSAC GF-6 phosphorus cap at 800 ppm constrains ZDDP treat rate, driving careful chemistry balance. This guide covers ZDDP types, synthesis chemistry, treat rates by service, and Indian sourcing.
| Service | ZDDP Type | ZDDP Treat % (finished) | P (ppm finished) | Zn (ppm finished) |
|---|---|---|---|---|
| API SP / ILSAC GF-6 PCMO | Mixed Pri/Sec 50:50 | 0.85-1.05% | 780-800 | 850-950 |
| API SN+ PCMO | Mixed Pri/Sec 50:50 | 0.90-1.10% | 800-900 | 900-1000 |
| API SN PCMO | Mixed Pri/Sec 70:30 sec | 0.85-1.10% | 800-1000 | 900-1100 |
| API SM (legacy) | Sec dominant | 0.95-1.30% | 900-1200 | 1000-1300 |
| API CK-4 HDD | Primary dominant | 1.10-1.40% | 1100-1200 | 1200-1300 |
| API CJ-4 HDD | Primary dominant | 1.00-1.30% | 1000-1200 | 1100-1300 |
| API FA-4 low-VG HDD | Primary dominant | 1.10-1.40% | 1100-1200 | 1200-1300 |
| Industrial Hydraulic HV / HVI | Mixed Pri/Sec | 0.30-0.60% | 250-450 | 280-500 |
Neither is universally better — they serve different roles. Primary alkyl ZDDP (made from primary alcohols like 2-ethylhexanol, isooctanol, butanol) has higher thermal decomposition temperature (~220 °C) and slower tribofilm build but better thermal stability — used in HDD CK-4 / FA-4 where oil temperature stays high. Secondary alkyl ZDDP (made from 4-methyl-2-pentanol, 2-butanol, isopropanol) decomposes earlier (~180 °C) and builds anti-wear tribofilm faster — used in PCMO API SP for cold-start cam wear protection.
Most commercial DI uses a mixed primary/secondary blend to get both properties.
No, but it tightly caps phosphorus at 800 ppm in finished oil — same as API SP. ZDDP is still the workhorse anti-wear; you just can't use as much. Mixed primary/secondary ZDDP delivers Sequence IVB cam wear and Sequence X chain wear performance within the 800 ppm P budget. GF-6 also added the Sequence VIII / Sequence VIE-LP / Sequence IX tests where ZDDP balance matters.
The likely future direction (GF-7, GF-8) holds the 800 ppm cap but adds tighter chain wear and LSPI tests — ZDDP-plus-MoDTC-plus-borated-dispersant becomes the standard combination.
Ashless dithiophosphate (ADTP) replaces the Zn in ZDDP with an amine cation — giving the dithiophosphate anti-wear function without contributing sulfated ash. Used in low-SAPS ACEA C-class formulations where sulfated ash is capped at 0.5-0.8%.
ADTP delivers ~80-90% of ZDDP's anti-wear performance per atom of P; the trade-off is the loss of Zn's secondary antioxidant and corrosion-inhibitor function. Most ACEA C3 formulations use partial ADTP replacement (50:50 ZDDP:ADTP) rather than full ZDDP elimination.
Yes — industrial hydraulic AW (anti-wear) is the second-largest ZDDP volume after engine oil. ISO HV / HVI hydraulic fluid uses 0.3-0.6% ZDDP at lower treat than engine oil (P content 250-450 ppm in finished hydraulic). Industrial gear oil, compressor oil and turbine oil use lower or no ZDDP — turbine R&O uses phenolic + aminic AO only (no AW).
Pump pass tests (Denison T6H20C, Vickers V104C, Eaton 35VQ25) drive the ZDDP treat rate in hydraulic.
Three constraints. (1) P limit by spec — API SP 800 ppm, GF-6 800 ppm, CK-4 1200 ppm, ACEA C3 800 ppm. (2) AW performance target — Sequence IVB cam wear < 90 µm avg, Four-Ball D4172 scar < 0.5 mm. (3) Cost — ZDDP is ₹500-700/kg, dominates the DI cost line.
In practice: API SP PCMO uses 0.9-1.1% ZDDP active (giving ~780-800 ppm P); CK-4 HDD uses 1.0-1.4% (giving ~1100-1180 ppm P); ACEA C3 uses 0.6-0.8% ZDDP plus 0.2-0.3% ADTP to hit 800 ppm P at 0.7% sulfated ash.
Branded ZDDP from Lubrizol (LZ 1395, 1097, 5034), Afton HiTEC (7197, 7169), Infineum (C9425, C9420), BASF Irgalube TPPT, RT Vanderbilt Vanlube 829, Adeka Sakura-Lube. Lands in India at ₹450-650/kg.
Indian-blended ZDDP from select Indian additive houses and Lubechem custom equivalents land at ₹320-450/kg — 30-35% saving. Custom ZDDP equivalents pass D4172 four-ball wear and Falex pin-and-vee EP within 3% of branded baseline.
For mid-volume blenders (1,000-10,000 MT/year finished oil) using >50 MT/year of ZDDP, custom equivalent saves ₹15-30 lakh per year on additive cost. The ZDDP manufacturing route (alcohol + P2S5 → dithiophosphoric acid → neutralisation with ZnO) is public-domain.
Indian blenders typically don't manufacture ZDDP in-house — instead they buy custom-blended ZDDP from a regional additive house with the formulation IP owned by the blender, OR they buy custom DI package with the ZDDP already embedded. Both routes deliver the saving.
ZDDP thermal decomposition releases volatile phosphate species that can deposit in the EGR / catalyst path. NOACK D5800 volatility (1 hr @ 250 °C, vacuum) is the standard test — API SP / GF-6 cap NOACK at 15% max. Primary alkyl ZDDP has lower NOACK contribution (better thermal stability); secondary alkyl ZDDP has slightly higher.
Custom DI uses primary-rich ZDDP in HDD CK-4 where NOACK matters more, and mixed pri/sec in PCMO API SP where cold-start AW matters more.
Share your target service (API SP, CK-4, ACEA C3, industrial hydraulic), P / sulfated ash budget and volume. We respond within one business day with a ZDDP selection plan and cost.