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API CK-4 vs FA-4: What Indian HDD Fleets Should Actually Buy

CK-4 is backwards compatible with older diesel hardware; FA-4 is a lower HTHS fuel-economy oil for specified modern engines only. Pouring FA-4 into a mixed Indian fleet is how you get warranty arguments. 15W-40 CK-4 remains the workhorse; 10W-30 CK-4 is the upgrade path.

By Er. Manoj Kumar, founder & chief formulator Published 24 Oct 2026 9 min read

Conceptual illustration of lubricant laboratory work; not a photograph of Lubechem facilities or measured results.

Direct answer

CK-4 is backwards compatible with older diesel hardware; FA-4 is a lower HTHS fuel-economy oil for specified modern engines only.
CK-4 and FA-4 are not two names for the same diesel oil. FA-4 is a lower HTHS, fuel-economy category that is not backward compatible with every older diesel. Indian mixed fleets still live on CK-4 / CI-4 Plus more often than FA-4. Do not pu
Name the test method on any number that reaches a TDS.
Patents and papers are prior art, not a product Lubechem sells.
Written for Fleet managers and HDD oil blenders.

HTHS, soot and aftertreatment in one table

HTHS, soot and aftertreatment in one table. CK-4 is backwards compatible with older diesel hardware; FA-4 is a lower HTHS fuel-economy oil for specified modern engines only. Pouring FA-4 into a mixed Indian fleet is how you get warranty arguments. 15W-40 CK-4 remains the workhorse; 10W-30 CK-4 is the upgrade path.

CK-4 and FA-4 are not two names for the same diesel oil. FA-4 is a lower HTHS, fuel-economy category that is not backward compatible with every older diesel. Indian mixed fleets still live on CK-4 / CI-4 Plus more often than FA-4. Do not put FA-4 in a CK-4 crankcase because a brochure said ‘latest API’.

The reader is Fleet managers and HDD oil blenders. Search phrases around “API CK-4 vs FA-4” should land on a decision: duty, method, purge, SKU sequence — then a link to the manufacturing page, not a second SOP.

Which Indian OEM manuals say FA-4

Which Indian OEM manuals say FA-4. CK-4 is backwards compatible with older diesel hardware; FA-4 is a lower HTHS fuel-economy oil for specified modern engines only. Pouring FA-4 into a mixed Indian fleet is how you get warranty arguments. 15W-40 CK-4 remains the workhorse; 10W-30 CK-4 is the upgrade path.

BIS IS 13656 overlay

BIS IS 13656 overlay. CK-4 is backwards compatible with older diesel hardware; FA-4 is a lower HTHS fuel-economy oil for specified modern engines only. Pouring FA-4 into a mixed Indian fleet is how you get warranty arguments. 15W-40 CK-4 remains the workhorse; 10W-30 CK-4 is the upgrade path.

How a blender dual-lines CK-4 without contaminating FA-4

How a blender dual-lines CK-4 without contaminating FA-4. CK-4 is backwards compatible with older diesel hardware; FA-4 is a lower HTHS fuel-economy oil for specified modern engines only. Pouring FA-4 into a mixed Indian fleet is how you get warranty arguments. 15W-40 CK-4 remains the workhorse; 10W-30 CK-4 is the upgrade path.

Lubechem will not invent a client list or a certificate. If the next step is a trial, send the duty brief. If the next step is legal clearance of a filing, that sits with a patent attorney.

What this page is for

Comparison the SAE grade pages cannot host without cannibalising each other. Images are labelled conceptual illustrations. Patents and papers are cited so you can go read them.

Bench screens before anyone argues about a brand name

Question	Method	Decision
Is the grade even itself?	D445, CCS/MRV if engine, VI	Fix KV before additive heroics
Will it stay put?	Noack, flash, pour, foam	Volatility and air release kill more launches than TBN
Will it protect metal?	D4172, D2783, rust, copper strip	EP is not antiwear; do not confuse them
Will it live?	Oxidation, RPVOT, PDSC, field drain	A 4-ball pass is not a 500-hour drain

People-first note: this is dated editorial for decision-making. It is not a scaled rewrite of the manufacturing pages, and it is not legal or certification advice.

Questions plants actually ask

Is API CK-4 vs FA-4 a drop-in for whatever we run today?

Almost never. Thickener family, base-oil viscosity, NLGI grade and additive response all have to be matched to the duty. A purge plan comes before a plant-wide switch. Compatibility charts are screens, not guarantees.

Can we put API CK-4 vs FA-4 on the TDS because a patent or paper mentioned it?

No. Patents are prior art. Papers are evidence under stated conditions. A TDS line has to be backed by a method you actually ran, on oil you actually stock, at a treat you can buy twice.

Who owns the formula if Lubechem develops it?

Ownership is the contract. The practice is independent formulation with IP transfer as scoped — not a branded additive package you can never leave. Ask for the assignment language before the first kettle.

What should Fleet managers and HDD oil blenders send in the first brief?

Duty (load, speed, water, temperature, relube), the current TDS and fail mode, target specs (IS / ASTM / OEM), and whether the product is sold, used in-house, or exported. Photographs of the failed component help more than adjectives.

Literature and prior art

Citations below are orientation, not a freedom-to-operate opinion. Lubechem does not copy claimed compositions and does not treat a patent as a product endorsement.

ASTM D445 kinematic viscosity — grade identity, not film strength
ASTM D4172 / D2783 wear and EP — bench screens, not a field duty cycle
API 1509 base-oil groups — saturates, sulfur, VI — not a performance licence
SAE J300 — engine-oil viscosity grades