Best Diesel Engine Oil
for Semi Trucks
AMSOIL Signature Series Max-Duty 15W-40 (DME) is the top pick for Class 8 diesel engines. API CK-4 certified, approved for Cummins, Detroit, Volvo, Mack, and PACCAR — it runs extended drain intervals up to 75,000 miles with oil analysis. ADP is the value alternative when drain intervals are conventional. What you run depends on your engine, OEM spec, and drain strategy.
Top Picks
Two AMSOIL products cover the entire Class 8 diesel market. The difference is drain interval and price.
AMSOIL Signature Series Max-Duty 15W-40
Extended drain engine oil engineered for Class 8 operators running 50,000–75,000 mi intervals with oil analysis. 6× wear protection vs industry standard.
- Cummins CES 20086 approved
- Detroit Fluid Spec 93K222
- Volvo VDS-4.5 / Mack EOS-4.5
- PACCAR CK-4 approved
- Allison TES-295
AMSOIL Heavy-Duty Synthetic Diesel Oil 15W-40
Full-synthetic at a lower price point. Conventional drain intervals. Allison TES-295 approved — solid pick for fleets with strict drain schedules or mixed equipment.
- API CK-4 certified
- Allison TES-295
- 4× wear protection vs industry standard
- Cummins, PACCAR, Detroit compatible
API Specs: CK-4 vs FA-4
Both specs launched in 2016 under API PC-11. They are not interchangeable.
| Feature | CK-4 | FA-4 |
|---|---|---|
| HTHS Viscosity | ≥ 3.5 mPa·s | 2.9–3.2 mPa·s |
| Fuel Economy Benefit | Minimal | Yes (0.4–1.5%) |
| Backward Compatible | Yes — CI-4, CH-4, CG-4 | No — 2017+ specific engines |
| Primary Use | All Class 8 diesel engines | Volvo D13, Mack MP8, Detroit DD-series (2017+) |
| Safe for Older Equipment | Yes | No — check OEM spec |
| Default Choice | Yes | Only when OEM approves |
Full breakdown: CK-4 vs FA-4 | Which Diesel Oil Spec Does Your Engine Actually Need →
Viscosity Grades for Semi Trucks
Most Class 8 engines run 15W-40 year-round. Cold-climate and fuel-economy applications shift the grade.
Standard grade for all major OEMs. Works from –13°F to extreme heat. Universal compatibility with CK-4 and most FA-4 engines.
Better cold cranking below –4°F. Minor fuel economy gain. Approved by Cummins, Volvo, Detroit. Confirm OEM spec before switching.
Sub –22°F applications. Northern Canada, mountain routes in winter. Use only where OEM approves — not universally sanctioned.
Older high-mileage engines with looser tolerances. Uncommon in modern fleets. Ask your OEM before using in late-model engines.
Viscosity selection by temperature range: Semi Truck Oil Weight Chart →
By Engine | OEM Oil Specs
Every major Class 8 engine has a specific proprietary spec layered on top of API CK-4. Meeting API alone isn’t enough — the engine needs its OEM approval.
Proprietary spec covering oxidation, soot handling, and wear. FA-4 not approved on most applications. 15W-40 primary.
Detroit’s DFS 93K222 covers 2017+ engines. FA-4 is approved on 2017+ models with EGR + SCR emissions. Pre-2017: CK-4 only.
VDS-4.5 is Volvo’s CK-4 equivalent. FA-4 approved on 2021+ FE (Fuel Efficiency) D13 only. Non-FE D13: CK-4 with VDS-4.5.
EOS-4.5 is Mack’s CK-4 equivalent. FA-4 NOT approved for MP8. 15W-40 is the only recommended grade.
PACCAR uses no proprietary oil spec. Any API CK-4 product qualifies. FA-4 not approved. 15W-40 standard grade.
International’s proprietary spec (MS-12633) on some models. A26 and LT engines — confirm spec year. 15W-40 CK-4 approved across the board.
Drain Intervals | OEM vs Extended
OEM drain intervals are minimums built around conventional oil. Full synthetic with oil analysis can safely extend those numbers — significantly.
| Application | OEM Interval | Extended (w/ Oil Analysis) |
|---|---|---|
| Highway — Cummins X15 | 25,000 mi / 500 hr | 50,000–75,000 mi |
| Highway — Detroit DD15 | 25,000 mi | 50,000–75,000 mi |
| Highway — Volvo D13 | 30,000 mi (Flexi program) | 50,000–75,000 mi |
| Highway — Mack MP8 | 25,000 mi | 50,000–60,000 mi |
| Severe / Vocational | 10,000–15,000 mi | 25,000–40,000 mi w/ analysis |
| Urban / Stop-Go | 7,500–10,000 mi | 15,000–20,000 mi w/ analysis |
Extended drain intervals require: full-synthetic oil (DME or equivalent), periodic oil analysis, and no coolant/fuel contamination. Don’t extend on guesswork — test the oil.
Oil Analysis for Semi Trucks | How to Extend Drain Intervals Safely →
AMSOIL vs. The Competition
Head-to-head data on the brands Class 8 fleets actually use.
Frequently Asked Questions
Ready to Switch?
AMSOIL DME delivers the lowest cost-per-mile for Class 8 fleets running extended drain intervals. Order direct from an authorized dealer — no dealer markup, no middleman.
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