5W-30 FA-4 Diesel Oil for Semi Trucks
GHG17 Engines — When FA-4 Is Right and When It Isn’t
5W-30 FA-4 is the preferred grade for GHG17 Detroit DD-series engines (DD13, DD15, DD16) using DFS 93K222 specification. It provides measurable fuel economy benefit over CK-4 15W-40 on GHG17 platforms — typically 0.5–1.0%. FA-4 is NOT approved for Cummins X15/ISX15, Volvo D-series, Mack MP-series, or any pre-2017 engine. Running FA-4 in a non-approved engine risks oil pressure faults and inadequate film protection.
What FA-4 Means
FA-4 is an API category introduced in 2016 alongside CK-4. The key difference is HTHS viscosity — FA-4 operates at 2.9–3.2 mPa·s vs CK-4’s minimum 3.5 mPa·s. Lower HTHS means a less viscous oil film under high-temperature, high-shear conditions.
GHG17 engines designed for FA-4 have tighter tolerances specifically engineered to work with lower film thickness. Older engines — and most current non-GHG17 platforms — were not. Putting FA-4 in an engine designed for CK-4 is not interchangeable; it’s a downgrade in film protection.
Where FA-4 Is Approved
WARNING: FA-4 must only be used in engines that explicitly approve it. Using FA-4 in a CK-4-only engine (Cummins, PACCAR, Volvo standard, Mack standard) can cause oil pressure faults and long-term wear damage.
| Engine | OEM Spec | FA-4 Approved? |
|---|---|---|
| Detroit DD13 GHG17 | DFS 93K222 | Yes — preferred |
| Detroit DD15 GHG17 | DFS 93K222 | Yes — preferred |
| Detroit DD16 GHG17 | DFS 93K222 | Yes — preferred |
| Cummins X15 | CES 20086 | No |
| Cummins ISX15 / ISX12 | CES 20081 | No |
| Volvo D13 (standard) | VDS-4.5 | No |
| Volvo D13 (2021+ FE) | VDS-5 | Yes |
| Mack MP8 (standard) | EOS-4.5 | No |
| Mack MP8 (2021+ FE) | EOS-5 | Yes |
| PACCAR MX-13 | CK-4 | No |
| International A26 | CK-4 | No |
The Fuel Economy Case
On a GHG17 Detroit fleet, switching from CK-4 15W-40 to FA-4 5W-30 produces a real, documented fuel economy improvement. Detroit publishes a 0.4–1.0% improvement in fuel economy. Across a fleet running long-haul miles, that compounds meaningfully.
The math only works when the engine is designed for it. An FA-4 upgrade on a GHG17 Detroit is a legitimate fleet efficiency tool. The same oil in a Cummins X15 is a liability.
Recommended AMSOIL Product
Frequently Asked Questions
What engines can use 5W-30 FA-4?
GHG17 Detroit DD-series (DD13, DD15, DD16) with DFS 93K222 spec. Specific 2021+ fuel-efficient Volvo and Mack engines with VDS-5/EOS-5. No other Class 8 engines currently approve FA-4.
Can I put FA-4 in my Cummins X15?
No. Cummins has not approved FA-4 for any X15 or ISX engine. CK-4 only.
Is FA-4 better than CK-4?
For approved engines: yes, measurable fuel economy benefit. For non-approved engines: no — lower HTHS is a liability. The question is whether your specific engine approves it.
Will FA-4 hurt my engine if used by mistake?
Potentially. The lower film strength of FA-4 is not a problem for engines designed around it, but in engines with older tolerances, it can cause increased wear over time. If the wrong oil was used for one drain interval, switch to the correct spec at the next change and monitor.