What It All Means

Elemental Analysis

Ferromagnetic Analysis

Infrared Analysis

Particle Counting

Titration Analysis



Fuel Dilution 


Elemental Analysis

Elemental Analysis of oil is usually performed using Inductively Coupled Plasma (ICP) spectroscopy.  The units reported are milligrams per kilogram (mg/kg) - aka parts per million (ppm) for convenience. 

For solids such as filter debris or grease, for fuel and for water contaminated samples we may use an X-Ray Fluorescence machine (XRF).  This is an alternative method of elemental analysis that also reports in mg/kg.   

XRF cannot detect the first 10 elements in the periodic table - including Boron and Lithium which ICP can detect.  However XRF can detect Chlorine and Sulfur and many more which ICP cannot.  ICP is limited to particles less than 10 micron in size (typical filtered oil).  XRF is not limited by particle size and may detect more than ICP if there are larger particles present.  For most oils with no abnormal particles, ICP and XRF will give essentially the same elemental analysis which is why we share the same analyte fields to allow comparison and trending.  The reason we switch from ICP to XRF if a sample is heavily contaminated with water is because the water can boil and extinguish the plasma spark and give false results.  In cases of water contamination it is also useful to have the Chlorine content, especially in marine samples where we may want to identify if the leak is salt water or coolant.

Symbol Name Typical Source
Ag Silver Some large marine and locomotive engines have used silver in bearings and require zinc-free engine oil to avoid silver corrosion damage.
Al Aluminium Widely used metal in many equipment compartments.  Dirt, dust, Sand often contains alumium oxide (alumina) which accompanies the silicon dioxide (silica). 
B Boron Boron based additives are used by some oil makers for their antiwear properties.
Ba Barium Barium Sulfonate is an anti-rust addtive used in some oil formulations.  Barium may also be an alloy metal. 
Ca Calcium Calcium Sulfonate is a popular detergent additive in many oil formulations.
Cd Cadmium Cadmium may be found in some solder or bearing metal alloys or electroplated parts.
Cl Chlorine Chlorine is useful for identifying salt water (Sodium Chloride).
Cr Chromium Chromium is commonaly used as an alloy to strengthen steel or provide a hard coating.  
Cu Copper Copper is often used in coolers.  Bronze (a copper and tin alloy) is often used for bushes, bearings, thrust washers, friction plates and other soft metal applications.
Fe Iron Iron or steel components are widely used in most equipment types.
K Potassium Potassium additives may be found in some oils and coolants.
Li Lithium Lithium complex greases are popular due to their high temperature melting points.  Unwanted high temp grease in an oil compartment can block oil galleries.
Mg Magnesium Magnesium sulfonate is a popular detergent additive often used instead of or together with calcium sulfonate detergent.
Mn Manganese Manganese may be a metal alloy.
Mo Molybdenum Molybdenum additives are used in some oil formulations for anti-wear properties.
Na Sodium Sodium found in engine oils typically indicates a coolant leak, but in a marine environment this could be sea water ingestion.  Cleaning detergents and external contaminants can also contain sodium.
Ni Nickel Nickel may be a metal alloy or an electroplated coating.
P Phosphorus Phosphorus is found in popular oil additives such as zinc dithiophosphate Anti-Wear and Sulphur Phosphorus Extreme Pressure compounds.
Pb Lead Lead is a soft metal often used in plain bearings or solder.
S Sulfur Sulfur is often found in oil and oil additives.  NZ Diesel fuel s limited by law to a maximum of 10 mg/kg sulfur content.
Si Silicon Silicones may be used as anti-foam additives.  Dirt, dust and sand is typically silicon dioxide (silica) and is often accompanied with aluminium dioxide (alumina).  Also Silicone elastomers, fluids and sealants. 
Sn Tin Bronze is an alloy of copper and tin.  Tin is also used in solder and plain bearings and for plating metals.  
Ti Titanium Titanum is a strong lightweight metal used in aviation and racing applications.  Titanium anti-friction additives are used by some oil makers.  Titanium oxide is a popular whitener used in paint and plastic.  
V Vanadium Vanadium may be a steel alloy metal.  It may also be found in some marine bunker fuels.
Zn Zinc Zinc dithiophospate (ZnDTP or ZDP) is a very popular anti-wear additive in many lubricating oil formulations.  Some equipment makers will demand a minimum zinc content for this reason.  

Ferromagnetic Analysis

Most equipment components contain a lot of iron or steel and this is usually the major wear metal that is being considered.  Normal wear consists of microscopic particles much less that 10 micron in size, which would easily pass through a typical 10µm filter and is best monitored via ICP element analysis.  However, in cases of abnormal wear there can be larger particles or chunks of iron or steel metal which may not be detected by ICP.  For this reason most used oil test labs use a ferromagnetic Particle Quantifier machine which detects the larger particles of iron that tend to settle to the bottom of a sample.      

The particle quantifier "PQ" machine uses electromagnetic field coils and the entire sample bottle is placed in the machine which provides an index number. 

For oil samples from filtered compartments (engine, transmission, hydraulics etc) we would expect the PQ index to be below 10. 

For unfiltered gearboxes such as differentials and final drives we would expect the PQ index to be below 150. 

For large tandem drives that typically generate a lot of large wear particles we would accept up to 300. 

When the PQ index exceeds 300 we can expect large chunks of iron in the sample, and to prevent damage to some of our lab equipment we may choose not to run some tests.  The PQ index alone is suggesting that the compartment is experiencing abnormal wear and requires attention. 

Note that incorrect oil sampling technique (such as taking a sample from the dirty side of a filter housing) can cause high PQ index values which are misleading and do not represent the oil in the system.   

Infrared Analysis

 Fourier Transform Infrared (FTIR) analysis measures the absorption of infrared light through an oil sample.  The software identifies the absorption of IR energy across a spectrum of wavelengths.  Specific compounds have unique resonant frequencies due to their molecular bonds.  The software is programmed to look for specific compounds associated with known contaminants and to provide an index number that increases with absorption in that specific range.   

There are thousands of unique oil formulations in use, and each one has a unique FTIR signature from new.  During use oil and additives degrade and change in molecular structure and contaminants can enter the oil.  

The method we use is an Unsubtracted method which does not attempt to subtract the baseline signature from the results.  (For many of the samples we receive the oil type is unknown, or a mixture or misidentified.  A subtracted method would provide misleading data when the oil type is a false assumption). 

FTIR data needs to be interpreted with care - we use it as a lab screening tool and for general trending.  

Symbol Name Significance
St Soot Soot is a byproduct of incomplete combustion of hydrocarbon fuel that accumulates in engine oil.  If it is not removed or replaced the oil will increase in viscosity and eventually turn solid.
Oxi Oxidation Hydrocarbon oil exposed to air eventually oxides and forms other compounds that can create varnish, sludge etc.
Sul Sulfation When high sulfur fuels are burnt acids can be formed which enter the engine oil and cause it to become sulfated. (Not a problem with NZ ultra low sulfur diesel).
Nit Nitration If engines are running very hot and lean they oil may become nitrated from the nitrogen in air.  Can be a problem with some gas engines.


Particle Counting

ISO 4406 automatic laser particle counting allows the monitoring of particles in oil systems.  It is a useful tool to to measure the effectiveness of filters and establish contamination control. 

Laser particle counting does not identify what the particle is - it simply counts anything that interrupts the laser beam as being a particle.  This could be dirt or metal or paper or plastic, but it could also be water or air bubbles or undissolved oil additives.  The machine takes measured amounts of sample and optically counts the number of particles.  There are major two factors - quantity and size.   

Particle Quantity

The literal count of particles per 100ml can yield large numbers which are awkward to use.  For this reason the International Standards Organisation (ISO) have developed the 4406 coding system that assigns codes for specific categories of particle count.  Note that each code is basically doubling each time.  

ISO 4406 Code

Min Count

per 100mL

Max Count

per 100mL (inc)

1 1 2
2 2 4
3 4 8
4 8 16
5 16 32
6 32 64
7 64 130
8 130 250
9 250 500
10 500 1000
11 1000 2000
12 2000 4000
13 4000 8000
14 8000 16000
15 16000 32000
16 32000 64000
17 64000 130000
18 130000 250000
19 250000 500000
20 500000 1000000
21 1000000 2000000
22 2000000 4000000
23 4000000 8000000
24 8000000 16000000


Particle Size

A particle count is of little value unless the size of particles is defined.  The smaller the minimum size is defined the more particles have to be counted.  

A nominal 10 micron (10µm) filter is a very popular mesh size.   The ISO system has settled on 3 main "channels" of particle size for reporting purposes:  

>4µm Greater than 4 micron Often not used unless dealing with ultra fine filtered oil
>6µm Greater than 6 micron Many of these particles can be expected to pass straight through a 10 micron filter
>14µm Greater than 14 micron Most of these these particles should be stopped by a 10 micron filter


These codes are reported in a standard format that looks a little like a date format - for example 21/18/15

If 3 codes are used the format is >4/>6/>14

If 2 codes are used the format is >6/>14

Practical Application

On average if a particle count increases by one code the particle count has doubled.  It could be just one extra particle that bumps the count into the next category.  Or if the previous particle count was at the bottom of one category and increased to the top of the next category that could represent a 4 times increase in the particle count.  It is generally accepted that an increase of 1 code is not significant. 

A increase of 2 codes could be very significant as this would be at minimum a doubling in particle count or possibly as much as an 8 times increase.  On average an increase of 2 codes is a 4 times increase in particles.   

Individual equipment makers or contamination control engineers can decide on the maximum limit that they consider acceptable.  For example Caterpillar and other OEM consider that 18/15 for a filtered compartment is an acceptable maximum.  In order to achieve this it makes sense to ensure that new oil being put into that compartment is two codes lower (because 1 code does not allow for any significant increase).  This is the reason that Caterpillar and other OEM recommend that new oil should be filtered to 16/13 before use. 

Because optical particle counting does not differentiate the type of particles it should not be assumed that any particles counted are good or bad.  The words "clean" or "dirty" are frequently used when discussing particle counts but a large percentage of particles counted are beneficial oil additives.  Most unfiltered new oils from an unopened drum will have a relatively high particle count which is most likely from undissolved or agglomerated additives.  There may be a small amount of harmful metal and dirt but the majority of particles counted in new oil is particles that are supposed to be there.  In a working system with hot oil passing through gears and filters multiple times that additives get broken down and particles trapped in the filters and particles counts tend to improve over time.  However - if a filter blocks and goes into bypass the particle count may increase again. 

Equipment that contains wearing friction plates such as brakes or clutch packs may generate a lot of particles in normal operation.  Some friction plate materials such as cellulose don't contain any metals that would show up in elemental analysis, so a high particle count may be the only clue about excessive wear of those plates.        


Titration Analysis

 Titration is a method or process of determining the concentration of a dissolved substance in terms of the smallest amount of reagent of known concentration required to bring about a given effect in reaction with a known volume of the test solution. 

Titration tends to be expensive in time and materials and therefore these are optional tests that are not automatically included in the standard test kit cost.  In most cases these tests are not necessary or recommended because the standard tests are adequate for the purpose.  However there are some specific applications where these tests may be essential and they can be purchased either as a special test kit or as additional tests.

Symbol Full Name Units Method Significance
TAN Total Acid Number mg KOH/g ASTM D664 For condeming oil which has become excessively acid with oxidation or contaminants. 
TBN Total Base Number mg KOH/g ASTM D2896 For monitoring depletion of alkaline reserves in engines running  fuels such land fill gas or high sulphur marine fuel.  
H20 ppm Water by Karl Fischer mg/kg ASTM D6304 For monitoring water content below 0.1% (1000 ppm) where small amounts of water are critical (e.g. refrigeration compressors)



Viscosity is a measure of the ability of a fluid to resist movement and can be thought of as a measure of the internal friction of a fluid.  Viscosity is commonly described in terms of "thick" or "thin" which is not strictly correct but useful for discussion purposes.  Water is very low viscosity and pours freely.  Honey is highly viscous and pours very slowly.  As honey is heated up it gets less viscosu ( 'thinner') and pours faster.    

Viscosity is the most important physical property of a lubricant as it affects it's ability to flow to where it is needed and to stay where it is needed.  Viscosity changes exponentially with temperature so it is essential to measure it at a agreed temperature.  The SAE viscosity grade system used 100°C.  The ISO viscosity grade system uses 40°C.   

Gough Analytical reports Kinematic Viscosity in centistokes at 40 degrees celcius. 

If necessary we can test viscosity at 100°C or other temperatures as additional tests (not included in standard cost).

The reasons we use 40°C instead of 100°C are:


  • The ISO viscosity grades are based around 40°C
  • Most oil makers publish typical new V40 viscosity as well as V100
  • Oil flows slower at cooler temperatures so the accuracy can be better for V40
  • Contaminants such as water and fuel can boil vigorously at 100°C and give false results


There are many SAE multigrade oils that look the same at 100°C but we can tell them apart at 40°C.  For example a monograde SAE 40, a 15W40 and a 0W-40 could all have the same V100 as they are all SAE 40 oils which is defined at 100°C.  However, at 40°C the difference becomes very obvious as the better multigrades have much lower V40 results (which is an indication that they are not going to be too thick to flow in cold temperature applications).  

Oils are sold in different viscosity grades to suit different temperature, load and speed conditions.  The use of the wrong grade could cause failure especially in extreme conditions.   Some contaminants (such as soot and glycol) can cause oil to thicken excessively.  Other contaminants (such as fuel or leaking hydraulic oil) can cause oil to thin excessively.  Changes in viscosity can indicate serious problems.  It is important to correctly identify the oil types and grades being used to allow accurate monitoring of viscosity changes. 



Water is a common contaminant that can harm equipment.  Typical sources of unwanted water can be:

  • Condensation of moisture from the air
  • Rain water
  • Sea Water (marine)
  • Cooling system leaks
  • Combustion gas - cylinder blowby

For most practical engineering purposes a small amount of water is inevitable and acceptable as long as it does not exceed 0.1% (1000 ppm).  

For standard oil testing Gough Analytical reports H2O% which is the percentage of water estimated by the industry standard Hot Plate Crackle Test.  This provides a good indication when the water content exceeds 0.1%.  

Where it is critical to know the water content more accurately below 0.1% Gough Analytical reports H2Oppm which is water content in mg/kg (parts per million) by the ASTM D6304 Karl Fischer titration method.   


Fuel Dilution

Excessive fuel dilution in a diesel engine can result from leaking fuel injectors or pump failures.  There is usually a small acceptable amount of fuel dilution in normal used engine oil.  The various engine makers can have different levels of acceptable fuel dilution for certain engine types.  There are also different methods of measuring fuel dilution that may give slightly different results. 

Excess fuel dilution drops the viscosity and also drops the flash point of an engine oil.  Gough Analytical looks for both a significant drop in viscosity and flash point to provide an estimation of the fuel percentage.  Where fuel dilution is detected this is reported as Fuel to the nearest percentage.  This fuel percentage is derived from a flash point correlation based on NZ diesel.