API CK-4 vs. FA-4: Choosing Diesel Engine Oil

API CK-4 is a broad heavy-duty diesel category designed for high-speed four-stroke engines and is commonly used in current and many older applications where the manufacturer permits it. API FA-4 is a lower-HTHS category for selected newer on-highway engines and is not interchangeable or backward compatible with CK-4.¹

Do not standardize a fleet on FA-4 without an engine-by-engine approval check.

What is API CK-4?

CK-4 oils are formulated for diesel engines using fuel with sulfur content up to 500 ppm, although API advises consulting the engine manufacturer about intervals when sulfur exceeds 15 ppm.¹

CK-4 protects against oxidation, viscosity loss, aeration, catalyst poisoning, particulate-filter blocking, wear, deposits, and soot-related viscosity increase. It is available in several viscosities and may carry OEM approvals.

What is API FA-4?

FA-4 covers certain XW-30 oils for selected high-speed four-stroke diesel engines designed around 2017-model-year on-highway greenhouse-gas standards. API defines its HTHS viscosity range as 2.9–3.2 mPa·s and limits the intended fuel to 15 ppm sulfur.¹

The lower HTHS can support fuel-efficiency goals in engines designed and approved for it. It is not a universal “newer is better” replacement.

What are the key differences?

Factor	API CK-4	API FA-4
Intended fleet scope	Broad current heavy-duty category	Selected newer on-highway engines
HTHS	Conventional heavy-duty range by grade	2.9–3.2 mPa·s
Backward compatibility	Often covers earlier diesel categories, subject to OEM guidance	Not backward compatible with CK-4/CJ-4/CI-4/CH-4
Viscosity	Multiple grades	Certain XW-30 grades
Fuel sulfur	Up to 500 ppm with interval restrictions	Up to 15 ppm
API Donut	CK-4 service mark	Distinct FA-4 portion for identification

Can FA-4 be used in an older truck?

Only if the engine manufacturer explicitly approves it. API’s instruction is clear that FA-4 is not interchangeable with CK-4 or prior categories.¹

Some newer fleet engines may allow both categories under different conditions. Others allow CK-4 only. Use model-year and engine-specific guidance.

Can CK-4 be used in an FA-4-approved engine?

Many manufacturers allow CK-4 as an alternative in selected engines, sometimes with a fuel-economy tradeoff. That permission and the viscosity must come from the engine maker.

Volvo Trucks, for example, maps VDS-4.5 to CK-4 and VDS-5 to FA-4 in current guidance and shows model-year-specific recommendations.² Do not apply Volvo’s matrix to another engine brand.

Which category does Inforca currently document?

Inforca’s active heavy-duty products include CK-4 options:³

• MANNOL TS-14 UHPD 15W-40, MN7114;
• MANNOL TS-17 UHPD 5W-30, MN7117;
• MANNOL TS-18 15W-40;
• MANNOL TS-16 UHPD 5W-40;
• PureGuard 15W-40 synthetic-blend heavy-duty, PG206.

The current Inforca knowledge files do not document an active API FA-4 SKU. Do not propose CK-4 as FA-4 or claim FA-4 availability without adding a verified product record.

How should a mixed fleet manage CK-4 and FA-4?

Use a controlled matrix:

1. List every engine make, model, year, and unit ID.
2. Record CK-4, FA-4, or dual permission.
3. Record required OEM approval and viscosity.
4. Separate FA-4 storage and dispensing if misapplication is possible.
5. Label fill points and service carts.
6. Train technicians on the distinct API Donut.
7. Review oil-analysis and interval rules by engine family.

If the fleet cannot reliably prevent cross-fill, the operational risk may outweigh a fuel-economy opportunity.

Frequently asked questions

Is FA-4 better than CK-4?

No. It is a different category for engines designed to use lower HTHS oil.

Is CK-4 backward compatible with CJ-4?

Often, but API says diesel backward compatibility is not universal. Confirm the engine maker and fuel sulfur.

Is every 10W-30 diesel oil FA-4?

No. Both CK-4 and FA-4 products can be XW-30. Read the API Donut.

Can FA-4 be mixed with CK-4?

Do not deliberately mix them. The resulting blend has uncertain category performance.

Does Inforca carry FA-4?

The current documented active portfolio does not verify an FA-4 product. Ask Inforca for current availability.

Send the engine list before standardizing

Send Inforca the engine makes, models and years, required API and OEM approvals, viscosity, fuel sulfur, duty cycles, monthly volume, and pack sizes. The team can map the documented CK-4 options and identify any FA-4 gap.

Sources

Footnotes

1. American Petroleum Institute, Oil Categories, accessed September 10, 2026. ↩ ↩² ↩³ ↩⁴

2. Volvo Trucks USA, D11, D13 and D16 Engine Oil Type and Quality, accessed September 10, 2026. ↩

3. Inforca International, Products: Engine and Motor Oils, accessed September 10, 2026. ↩