1. Viscosity Analysis
This is the most critical test, as viscosity is an oil's most important property.
What it Measures: The oil's resistance to flow at a specific temperature. It's reported in centistokes (cSt).
Why it's Important: An increase can indicate oxidation, oil degradation, or contamination (e.g., with a heavier oil). A decrease can signal contamination (e.g., with fuel or solvent) or shearing of viscosity index improvers in multi-grade oils. Both conditions can lead to inadequate lubrication and increased wear.
2. Fourier Transform Infrared (FTIR) Spectroscopy
A powerful and fast test that identifies the molecular "fingerprint" of the oil.
What it Measures: The presence of specific compounds by measuring how oil molecules absorb infrared light.
Why it's Important: Detects:
Oxidation: The breakdown of oil due to heat and oxygen.
Nitration: A byproduct of combustion gases, common in gas engines.
Soot: A primary contaminant in diesel engines.
Glycol: Coolant leaks from the cooling system.
Water Contamination.
Additive Depletion: The loss of key protective additives.
3. Acid Number (AN) and Base Number (BN)
These tests measure the corrosive potential of the oil.
Acid Number (AN): Measures the amount of acidic constituents in the oil. A rising AN indicates oil oxidation and the formation of corrosive acids.
Base Number (BN): Measures the oil's reserve alkalinity to neutralize acids. It's critical for engine oils. A falling BN means the oil is losing its ability to combat acids from combustion, leading to corrosion.
4. Elemental Spectroscopy
This test is the primary tool for detecting wear metals, contaminants, and additives.
What it Measures: The concentration of various elements in parts per million (ppm). It uses techniques like Atomic Emission Spectroscopy (AES) or Inductively Coupled Plasma (ICP).
Why it's Important:
Wear Metals: Iron (Fe), Chromium (Cr), and Aluminum (Al) indicate engine or component wear. Copper (Cu) and Lead (Pb) indicate bearing wear. Tin (Sn) can indicate piston or bearing wear.
Contaminants: Silicon (Si) suggests dirt/sand ingress. Sodium (Na) and Boron (B) can indicate coolant leaks.
Additives: Calcium (Ca), Magnesium (Mg), Zinc (Zn), and Phosphorus (P) are common detergent and anti-wear additives.
5. Particle Counting
This test quantifies contamination by solid particles and is essential for hydraulic and circulating oil systems.
What it Measures: The number and size distribution of particles in the oil, typically reported according to the ISO 4406:99 cleanliness code (e.g., 18/16/13).
Why it's Important: High particle counts are the leading cause of wear and failure in systems with tight clearances (e.g., hydraulic pumps, servo valves). It directly measures the effectiveness of filters.
6. Karl Fischer Titration
The most accurate method for measuring water content in oil.
What it Measures: The precise concentration of water, reported in parts per million (ppm) or percentage (%).
Why it's Important: Water is a major contaminant that causes oil degradation, additive depletion, corrosion, and impaired lubricant films. Even small amounts (a few hundred ppm) can be harmful.
7. Analytical Ferrography
This is a more advanced diagnostic test used when spectroscopy indicates a high level of wear.
What it Measures: It separates and analyzes wear particles by size and type, depositing them on a glass slide (ferrogram) for microscopic examination.
Why it's Important: It distinguishes between different wear modes:
Rubbing Wear: Normal, fine particles.
Cutting Wear: Long, spiraled particles from abrasive contamination.
Fatigue Spalls: Chunky particles from surface fatigue (e.g., bearing failures).
Severe Sliding Wear: Large, flat particles.
8. Crackle Test for Water
A simple, quick, and qualitative screening test for water.
What it Measures: The presence of free or emulsified water by applying a drop of oil to a hotplate (~250°F / 120°C). A crackling or popping sound indicates water is present.
Why it's Important: It's a fast field test to confirm a suspected water contamination issue before sending a sample for more precise (Karl Fischer) testing. It does not provide a quantitative result.
Summary Table
| Test | Category | Primary Purpose |
|---|---|---|
| Viscosity | Fluid Properties | Measures the oil's thickness and its change over time. |
| FTIR | Fluid Properties / Contamination | Detects oil breakdown products and specific contaminants. |
| Acid/Base Number | Fluid Properties | Measures the oil's corrosive potential and additive health. |
| Elemental Spectroscopy | Wear Debris / Contamination | Identifies and measures wear metals, contaminants, and additives. |
| Particle Counting | Contamination | Quantifies solid particle contamination levels. |
| Karl Fischer | Contamination | Precisely measures water content. |
| Analytical Ferrography | Wear Debris | Diagnoses the type and severity of wear mechanisms. |
| Crackle Test | Contamination | Quick field check for the presence of wat |