Quick Reference
SEMI TRUCK OIL WEIGHT CHART
The semi truck oil weight chart answer: most Class 8 diesels run 15W-40 CK-4.
If your engine is a Detroit DD13/DD15 (GHG17), Volvo D13, or Mack MP8 from 2017 or newer,
it takes 5W-30 FA-4 — not 15W-40. Full temperature ranges and OEM references below.
TEMPERATURE OPERATING RANGE
Where each grade operates reliably — from cold-start to sustained operating temp.
Lower W-number = better cold-start flow.
0°F
40°F
80°F
120°F
* Bars represent usable operating range. Always check OEM cold-start specification for your specific engine and ambient conditions.
CK-4 GRADE COMPARISON
All four CK-4 viscosity grades available for Class 8 diesel. 15W-40 covers the widest range of North American fleets.
★ Most widely used CK-4 grade in North American Class 8 fleets.
FA-4 VS CK-4 — WHICH SPEC DO YOU NEED?
FA-4 was introduced for GHG17-era engines specifically engineered to use lower-HTHS oil. CK-4 remains the standard for everything else.
- HTHS minimum: 3.5 mPa·s
- Covers Cummins, PACCAR, CAT, older Detroit
- Primary grades: 15W-40, 5W-40, 10W-30
- Backward compatible with older API specs
- Safe for mixed fleets with varied engine ages
- HTHS minimum: 2.9 mPa·s (intentionally lower)
- Detroit DD13/DD15 GHG17, Volvo D13, Mack MP8 (2017+), Mercedes OM471
- Primary grades: 5W-30, 10W-30
- Fuel economy improvement vs CK-4
- NOT backward compatible — do not mix
FA-4 oils have lower film strength (HTHS 2.9 vs 3.5 mPa·s). Using FA-4 in an engine
spec’d for CK-4 — such as Cummins X15, PACCAR MX-13, or CAT C15 — risks inadequate
bearing protection at operating temperature and will void most manufacturer warranties.
Always verify your engine’s emissions era before selecting an oil spec.
5W-30 FA-4 is the primary grade for GHG17 engines in most North American conditions.
10W-30 FA-4 is available for moderate climates where cold-start performance is less critical.
Both deliver the same fuel efficiency benefits — check your dataplate for emissions year first.
BY ENGINE — QUICK REFERENCE
Primary viscosity grade and FA-4 approval status for the eight most common Class 8 diesel engines in North America.
| Engine | Primary Grade | FA-4 Approved |
|---|---|---|
| Cummins X15 / ISX15 | 15W-40 CK-4 | No |
| Detroit DD15 (GHG17) | 5W-30 FA-4 preferred | Yes |
| Detroit DD15 (EPA10) | 15W-40 CK-4 | No |
| Volvo D13 (2017+) | 5W-30 FA-4 preferred | Yes |
| Mack MP8 (2017+) | 5W-30 FA-4 preferred | Yes |
| PACCAR MX-13 | 15W-40 CK-4 | No |
| CAT C15 | 15W-40 CK-4 | No |
| Mercedes OM471 | 5W-30 FA-4 | Yes |
Primary grades reflect OEM recommendations under typical North American conditions. Always verify against your engine’s operator manual and emissions compliance label.
WHAT HTHS MEANS — AND WHY IT MATTERS MORE THAN THE GRADE NUMBER
HTHS stands for High-Temperature High-Shear viscosity. It’s measured at 150°C under
shear stress — the conditions that closely resemble what happens in engine bearings at full load.
The W-grade tells you about cold starts. HTHS tells you about film strength when it counts.
Thicker film at operating temperature. Provides robust bearing protection for
high-output engines like the Cummins X15 and CAT C15. Required for any engine
not specifically approved for FA-4.
Intentionally thinner under shear. GHG17 engines are designed with tighter
tolerances to work with lower-HTHS oil — the tradeoff is measurable fuel economy gains.
Safe only in FA-4-certified engines.
A 5W-30 CK-4 and a 5W-30 FA-4 have the same cold-start and hot-viscosity grade numbers —
but different HTHS values. The grade number alone doesn’t tell you which spec the oil is.
Always check the API donut on the label for CK-4 or FA-4 before filling.
RECOMMENDED OIL FOR CLASS 8 DIESEL
AMSOIL makes a direct product for each spec. Both are formulated specifically for
heavy-duty diesel and exceed API minimum requirements.
CK-4 / 15W-40
Built for Cummins, PACCAR, CAT, and Detroit EPA10. Exceeds API CK-4 and
is backward compatible with CJ-4 engines. Handles extended drain intervals,
high-load cycles, and severe-duty applications.
15W-40
HTHS ≥ 3.5
FA-4 / 5W-30
Engineered for GHG17 Detroit DD13/DD15, Volvo D13, and Mack MP8 2017+.
Lower HTHS by design for measurable fuel savings. Meets API FA-4 and
exceeds Detroit Fluid Specification DFS 93K222.
5W-30
HTHS ≥ 2.9
FREQUENTLY ASKED QUESTIONS
North American operating conditions and is approved by Cummins, PACCAR, CAT, and older
Detroit engines. Newer Detroit DD13/DD15 (GHG17), Volvo D13, and Mack MP8 (2017+)
engines are designed for 5W-30 FA-4 to maximize fuel efficiency.
If you run a mixed fleet with older and newer engines, verify each engine’s spec separately —
they are not interchangeable.
temperature. 5W-30 FA-4 runs thinner (HTHS ≥2.9 mPa·s) by design — it reduces internal
friction in FA-4-certified engines for better fuel economy. The 5W-30 also flows better
in cold starts. FA-4 is not backward compatible: do not use it in engines spec’d for CK-4 only.
in moderate climates. It cannot be used in sub-freezing conditions below −4°F (−20°C).
Always check your engine’s operator manual — using an unapproved viscosity can void warranty coverage.
are designed for 5W-30 FA-4. EPA10-era DD15 engines use 15W-40 CK-4.
FA-4 is not approved for EPA10 DD15s — check your dataplate for the model year before filling.
When in doubt, pull the operator manual or contact Detroit directly.
the oil’s cold-cranking viscosity — how easily it flows during a cold start. Lower numbers
flow better at low temperatures, protecting bearings faster after startup. The number after
the W (30, 40) indicates kinematic viscosity at 100°C, representing the oil’s thickness
at operating temperature. A 15W-40 flows like a 15-weight at cold start and like a 40-weight
when fully warmed up.