API CK-4 vs CI-4 Diesel Engine Oil: DPF, Older Engines and Compatibility
API CK-4 and API CI-4 are diesel engine-oil performance categories. They do not replace the viscosity grade or manufacturer approval. A correct diesel oil must match the engine generation, emissions system, fuel sulfur level, service duty and every OEM requirement.
CK-4 and CI-4 at a glance
| Category | General position | Important caution |
|---|---|---|
| API CI-4 | Earlier heavy-duty diesel category used for engines from an older emissions generation | Can be unsuitable where a newer category or aftertreatment-compatible oil is required |
| API CK-4 | Current heavy-duty category designed for newer engines and improved protection | Follow OEM guidance, fuel-sulfur limits and required approvals |
| API FA-4 | Lower-HTHS XW-30 category for selected newer engines | Not interchangeable or backward compatible with CK-4/CI-4 unless the engine maker permits it |
Is CK-4 backward compatible with CI-4?
The American Petroleum Institute states that CK-4 oils exceed the performance criteria of CJ-4, CI-4 with CI-4 PLUS, CI-4 and CH-4 and can lubricate engines requiring those categories. That general category relationship does not cancel a manufacturer-specific approval, viscosity requirement, drain interval or fuel-sulfur restriction.
What about a diesel particulate filter?
Aftertreatment systems make oil chemistry especially important. Use the category and OEM approval specified for the exact engine. Do not assume an older CI-4 product is suitable for a DPF-equipped engine merely because the viscosity matches. Likewise, do not select oil only because the label says CK-4 if the engine requires another approval.
Older equipment and Cat DEO CI-4
Older Tier 3 and prior equipment without aftertreatment can specify CI-4-era products. Our separate Cat DEO 15W-40 CI-4 guide explains why the engine model, emissions tier and Cat recommendation must be confirmed before use.
Selection checklist
- Identify engine model, serial number and emissions tier.
- Check whether DPF, SCR or another aftertreatment system is installed.
- Match SAE viscosity and API category.
- Match every OEM specification or approval.
- Check fuel sulfur and drain-interval guidance.
Browse diesel and heavy-duty engine oils or send MAK Group the engine model and serial number.
Quick answers
Can CK-4 replace CI-4?
Often at the API category level, but only when viscosity, OEM requirements, fuel and service conditions also permit it.
Can CI-4 be used with a DPF?
Do not assume so. Follow the exact engine and aftertreatment requirement.
Is FA-4 the same as CK-4?
No. API states that FA-4 is not interchangeable or backward compatible with CK-4 and older categories.
Technical review and sources
Reviewed by: MAK Group Lubrication Specialists. Last reviewed July 23, 2026.
الخلاصة: CK-4 أحدث من CI-4 لكن لازم نطابق المحرك وDPF ومواصفة الشركة واللزوجة. FA-4 فئة مختلفة ومش بديل تلقائي.
