High Acid Number may arise from multiple operating, fluid, sampling or analytical causes. The pattern, rate of change and correlated evidence determine the most credible explanation.
Start with the observation
Confirm sample identity, method, units, service interval and historical baseline. A single abnormal parameter rarely confirms root cause, and a plausible explanation should predict other evidence that can be checked.
Differential diagnosis
| Possible cause | Supporting indicators | Confirming tests | Immediate response | Long-term corrective action |
|---|---|---|---|---|
| Oxidation | Oxidation | acid number | Compare with new-oil baseline | Correct the confirmed source rather than the isolated number |
| Acidic contamination | Varnish | ftir oil condition monitoring | Review oxidation controls | Establish a follow-up sampling point and timing |
| Wrong fluid | Viscosity change | kinematic viscosity | Compare with new-oil baseline | Document maintenance so the post-action trend can be evaluated |
Confirming and supporting evidence
Confirming tests
Supporting indicators
- Oxidation
- Varnish
- Viscosity change
Immediate and corrective actions
| Stage | Objective | Action |
|---|---|---|
| 1 · Verify | Confirm the observation is comparable | Check asset, compartment, sample point, units, method, interval, top-up and maintenance history. |
| 2 · Protect | Control immediate equipment or safety risk | Compare with new-oil baseline; Review oxidation controls |
| 3 · Diagnose | Find the source using independent evidence | Use acid number, ftir oil condition monitoring, kinematic viscosity and relevant inspection evidence. |
| 4 · Correct and confirm | Remove the cause and prove effectiveness | Correct the confirmed source rather than the isolated number; Establish a follow-up sampling point and timing; Document maintenance so the post-action trend can be evaluated |
- 01Compare with new-oil baseline
- 02Review oxidation controls
- 03Correct the confirmed source rather than the isolated number
- 04Establish a follow-up sampling point and timing
- 05Document maintenance so the post-action trend can be evaluated
False positives and context checks
- Non-representative sample
- Changed method or laboratory
- Recent top-up or overhaul
- Container or sampling-tool contamination
References and method context
References identify authoritative source families; they do not reproduce protected procedures or acceptance tables. Verify the current official edition before procedural or conformity use.