API FA-4 Diesel Engine Oil

The API FA‑4 category, introduced by the American Petroleum Institute in 2017, targets the latest generation of heavy‑duty diesel engines, especially those built to meet greenhouse gas (GHG) emission standards introduced around that time.

These oils are formulated specifically for select high-speed four-stroke diesel engines, delivering superior fuel economy and emission control, but are not backward-compatible with older categories like CK‑4, CJ‑4, CI‑4 PLUS, CI‑4, or CH‑4.

Key Technical Characteristics

• Lower HTHS viscosity: FA‑4 oils are blended to achieve a high-temperature, high-shear (HTHS) viscosity between 2.9 cP and 3.2 cP, which is lower than CK‑4’s typical ≥ 3.5 cP.
• Fuel efficiency gains: This reduction in HTHS viscosity enables easier flow at operating temperatures, reducing friction and resulting in measurable fuel economy improvements. In some cases, up to ~1% versus CK‑4, particularly with SAE XW‑30 grades.
• Emission and GHG benefits: FA‑4 oils help reduce fuel-derived greenhouse gas emissions and support modern emission systems, including diesel particulate filters and after-treatment hardware.

Protection & Durability

Despite being lower-viscosity, FA‑4 oils still uphold rigorous performance standards:

• They undergo the same oxidation and shear stability, aeration resistance, and wear protection testing as CK‑4 oils.
• Studies show FA‑4 delivers comparable hardware protection, even under heavy loads and high temperatures.
• FA‑4 oils are formulated for SAE 10W‑30 and 5W‑30 grades, balancing thin-film flow with robust wear control.

Compatibility & Use Guidelines

• Not suitable for older engines: FA-4 should only be used where the engine manufacturer explicitly allows its use. It is not for mixed or legacy fleets unless OEM approval is confirmed.
• Sulfur limits: Use only with ultra-low sulfur diesel (≤ 15 ppm), as higher sulfur content may impact after-treatment systems and oil longevity.
• OEM specifications: Engine makers often pair FA-4 with new engine specs (e.g., Cummins CES 20087, Detroit 93K223), while recommending CK-4 (CES 20086, 93K222) for broader backward compatibility.