API Diesel Engine Oil Classification — Heavy-Duty
API CK-4 Diesel Engine Oil — Spec, Engines & Product Guide
API CK-4 is the current diesel oil standard for most Class 8 engines in North America. It replaced CJ-4 in December 2016 with tighter requirements for oxidation resistance, shear stability, and aeration control — driven by higher EGR rates and more demanding emissions systems. If you're running a Cummins X15, Mack MP8, Volvo D13, PACCAR MX-13, or any pre-2017 Detroit, CK-4 is your spec.
Last reviewed: April 2026 · Based on API specification documentation, OEM service data, and AMSOIL technical data sheets
API CK-4 is the correct oil spec for Cummins X15 (CES 20086), Mack MP8 (EOS-4.5), Volvo D13 (VDS-4.5), PACCAR MX-13, International A26, CAT legacy engines, and all pre-2017 Detroit platforms. Primary viscosity: 15W-40. Detroit GHG17 engines (2017+ Cascadia) prefer FA-4 — CK-4 is acceptable there but not optimal. Not all CK-4 oils are equal: wear protection, volatility, and TBN vary significantly by product tier.
Replaced CJ-4
Viscosity
Viscosity
Volatility
Why API CK-4 Replaced CJ-4
Modern diesel engines became more demanding through the EPA10 and GHG17 emissions cycles — EGR rates climbed, aftertreatment systems added heat cycles, and soot loading increased. CJ-4 was designed for an earlier era of engine architecture. Three specific failure modes drove the CK-4 development mandate.
Every major engine OEM contributed failure data and test requirements. The result was a tighter spec in the areas that directly affect Class 8 engine longevity: shear stability, aeration resistance, and oxidation control at sustained high temperatures.
Backward compatible: CK-4 is fully approved for engines previously using CJ-4, CI-4+, CI-4, or CH-4. Upgrading to CK-4 from any of these is safe and generally beneficial.
What CK-4 Improved Over CJ-4
- ↑ Oxidation resistance — better thermal stability at sustained high operating temperatures; oil holds up longer before acid buildup and thickening
- ↑ Shear stability — oil holds viscosity grade under mechanical stress; critical for engines running high-shear turbocharger and valve train loads
- ↑ Aeration control — less air entrainment in the oil; air bubbles reduce film strength and cause metal-to-metal contact at high load
- ↑ Soot handling — better dispersant chemistry keeps EGR soot suspended as individual particles; prevents agglomeration into abrasive clusters
- ↑ Wear protection — tighter Detroit DD13 liner scuffing test requirement; harder pass/fail threshold than CJ-4
API CK-4 Minimums vs AMSOIL Product Tiers — 15W-40
The API minimum sets the floor. What matters is how far above the floor your oil lands. The table below compares the three AMSOIL diesel tiers in 15W-40 against the API CK-4 key thresholds.
| Property | API CK-4 Threshold | Sig. Series Max-Duty DME | HD Synthetic ADP | Commercial-Grade SBDF |
|---|---|---|---|---|
| Wear Protection | Detroit DFS scuffing test pass | 6× standard | 4× standard | 2× standard |
| Four-Ball Wear Scar (mm) | No API limit — comparison only | 0.45 | 0.50 | 0.53 |
| Noack Volatility (%) | 13% max | 6.9% | 7.1% | 6.6% |
| HTHS Viscosity (cP) | 3.5 min | 3.9 | 3.9 | 4.0 |
| TBN | No API minimum | 10.0 | 10.5 | 10.2 |
| Kinematic Visc. @ 100°C (cSt) | 12.5–16.3 | 15.4 | 15.3 | 15.4 |
| Pour Point (°C / °F) | — | −36 / −33 | −33 / −27 | −30 / −22 |
| Sulfated Ash (%) | 1.0% max | 1.0 | 1.0 | 1.0 |
Wear protection × multipliers based on third-party testing in the Detroit Diesel DD13 Scuffing Test for specification DFS 93K222. Four-Ball Wear (ASTM D4172) — lower scar = better. Noack Volatility (ASTM D5800) — lower = less burn-off. HTHS (ASTM D5481) — higher = thicker operating film.
Which Class 8 Engines Require API CK-4?
CK-4 covers the majority of current Class 8 platforms in North America. The key exception is Detroit GHG17 architecture — the 2017-and-newer Cascadia-generation DD13, DD15, and DD16 — where FA-4 is preferred.
| Engine | Common Truck | Oil Spec | OEM Standard | Primary Viscosity | AMSOIL Rec. |
|---|---|---|---|---|---|
| Cummins X15 | Peterbilt 579 / Kenworth T680 | CK-4 Required | CES 20086 | 15W-40 | DME / ADP |
| Mack MP8 | Mack Anthem / Pinnacle | CK-4 Required | EOS-4.5 | 15W-40 | DME / ADP |
| Volvo D13 | Volvo VNL | CK-4 Required | VDS-4.5 | 15W-40 | DME / ADP |
| PACCAR MX-13 | Peterbilt 579 / Kenworth T680 | CK-4 Required | API CK-4 | 15W-40 | DME / ADP |
| International A26 | International LT / RH | CK-4 Required | API CK-4 | 15W-40 | DME / ADP |
| Detroit DD13/DD15/DD16 (pre-2017) | Freightliner / Western Star | CK-4 Required | DFS 93K218 | 15W-40 / 5W-40 | DME / DEO |
| Detroit DD13/DD15/DD16 (2017+) | Freightliner Cascadia | FA-4 Preferred | DFS 93K222 | 5W-30 FA-4 | DHD 5W-30 |
| CAT C15 / C13 / 3406E | Vocational / legacy on-highway | CK-4 Required | ECF-3 | 15W-40 | DME / ADP |
Detroit GHG17 note: CK-4 meets DFS 93K222 and is acceptable in 2017+ Detroit engines, but FA-4 is the preferred spec. If you're running a post-2017 DD13, DD15, or DD16, see the engine-specific guide for the full FA-4 vs CK-4 breakdown for that platform.
CK-4 vs FA-4 — The Most Important Distinction in Class 8 Lubrication
Both specs were introduced simultaneously in December 2016. They are not the same — and using FA-4 in an engine that requires CK-4 compromises oil film thickness at operating temperature.
- HTHS Minimum3.5 cP
- Primary Viscosity15W-40
- Backward CompatibleYes — CJ-4 / CI-4+ / CI-4
- Cummins / Mack / VolvoRequired
- PACCAR / A26 / CATRequired
- Detroit GHG17Acceptable, not optimal
- AMSOIL ProductsDME / ADP / SBDF
- HTHS Target2.9–3.2 cP
- Primary Viscosity5W-30
- Backward CompatibleNo
- Cummins / Mack / VolvoNot approved
- PACCAR / A26 / CATNot approved
- Detroit GHG17Preferred spec
- AMSOIL ProductsDHD 5W-30 / DTT 10W-30
⚠ Do not use FA-4 in a Cummins X15, Mack MP8, Volvo D13, PACCAR MX-13, or International A26. FA-4's lower HTHS viscosity falls below what these engines were designed around. Film thickness at operating temperature will be insufficient. These platforms require CK-4 and do not approve FA-4.
Best AMSOIL CK-4 Oil for Class 8 Diesel Engines
Three tiers — all meet API CK-4. The tier determines how far above the protection floor you operate and whether extended drain intervals are on the table.
- Four-Ball Wear 0.45mm — lowest of the three tiers
- Noack 6.9% — minimal burn-off at sustained high temp
- Extended drain capable — up to 3× OEM / 60K mi
- Meets CES 20086, EOS-4.5, VDS-4.5, DFS 93K218, ECF-3, CK-4
- 76% less oil consumption than the API CK-4 limit
- Four-Ball Wear 0.50mm
- Full synthetic — not a blend
- OEM drain intervals
- Meets CES 20086, EOS-4.5, VDS-4.5, DFS 93K218, CK-4
- Step up from conventional or synthetic-blend
- Four-Ball Wear 0.53mm
- Greater than 50% synthetic content
- OEM drain intervals only
- Meets CES 20086, EOS-4.5, VDS-4.5, CK-4
- Upgrade from conventional diesel oil
| Product | Wear Protection | Drain Interval | Best For |
|---|---|---|---|
| Signature Series Max-Duty DME (15W-40) / DEO (5W-40) / DTT (10W-30) | 6× vs API standard | Up to 3× OEM — not to exceed 60,000 mi or 1 year | Owner-operators and fleets prioritizing maximum uptime and drain extension |
| Heavy-Duty Synthetic ADP (15W-40) / ADO (5W-40) / ADN (10W-30) | 4× vs API standard | OEM recommended intervals | Operators wanting full synthetic without committing to extended drains |
| Commercial-Grade SBDF (15W-40) / SBDT (10W-30) | 2× vs API standard | OEM recommended intervals only | Fleets stepping up from conventional oil on a budget |
Wear protection multipliers based on third-party testing in the Detroit Diesel DD13 Scuffing Test for specification DFS 93K222. Not all viscosities tested at each tier — see individual product data sheets.
⚠ AMSOIL AME 15W-40 (Synthetic Heavy Duty Diesel & Marine) is not on this list for a reason. AME does not carry approval for engines equipped with DPF or SCR aftertreatment systems. It is excluded from all GHG17-era Class 8 content. Use DME, ADP, or SBDF for any current on-highway Class 8 application.
API CK-4 Diesel Oil — Common Questions
Straight answers. No filler.