Test Predictors

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Introduction Viscosity Water/Coolant Contamination
Fuel Dilution Solids Fuel Soot
Oxidation Nitration Total Acid Number (TAN)
Total Base Number (TBN) Particle Count Wear Metal/Elemental Analysis
Quality Equipment Oil Analysis Program Oil Sampling Methods




Introduction

Oil analysis is a series of laboratory tests used to evaluate the condition of lubricants and equipment components. By studying the results of the oil analysis tests, a determination of equipment/component condition can be made. Primarily, this is possible because of the cause and effect relationship of the condition of the lubricant to the condition of the component sampled. Many of these cause and effect situations are outlined in this manual.

Oil performs several vital functions with many of them being interrelated. The ability of the oil to perform as designed can be determined by oil analysis. The following is a list of some primary lubricant functions that can be evaluated:

  • Friction control
  • Contaminant control
  • Hydraulic pressure
  • Temperature control
  • Corrosion control
  • Shock control
  • Wear control
  • Sealing function
The inspection or analysis of lubricating oil has been used to check and evaluate the internal condition of oil-lubricated equipment since the beginning of the industrial age. Early methods included smelling the oil to detect the sour odor of excess acidity, rubbing it between finger tips to check lubricity, and observing its color and clarity for signs of contamination.

Today, oil analysis programs use modern technology and laboratory instruments to determine equipment condition and lubricant serviceability. Oil analysis uses state of the art equipment and techniques to provide the user with invaluable information leading to greater equipment reliability.

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Viscosity

Viscosity is one of the most important properties of lubricating oil. Viscosity is a measurement of resistance to flow at a specific temperature in relation to time. The two most common temperatures for lubricating oil viscosity are 40°C and 100°C. Viscosity is normally evaluated with a kinematic method and reported in centistokes (cSt). In used oil analysis, the used oil's viscosity is compared to that of the new oil to determine whether excessive thinning or thickening has occurred.

Viscosity Index (VI) is the change in flow rate of a lubricant with respect to temperature. Oil with a high VI resists thinning at high temperatures. Use of high VI oil is recommended in engines and other systems that operate at elevated temperatures.


Cause
High Viscosity
  • Contamination soot/solids
  • Incomplete combustion-A/F ratio
  • Oxidation degradation
  • Leaking head gaskets
  • Extended oil drain interval
  • High operating temperature
  • Improper oil grade
Low Viscosity
  • Additive shear
  • Fuel dilution
  • Improper oil grade
Effect
High Viscosity
  • Increased operating costs
  • Engine overheating
  • Restricted oil flow
  • Accelerated wear
  • Oil filter bypassed
  • Harmful deposits/sludge
Low Viscosity
  • Engine overheating
  • Poor lubrication
  • Metal-to-metal contact
  • Increased operating costs
Solution
  • Check air-to-fuel ratio
  • Check for incorrect oil grade
  • Inspect internal seals
  • Check operating temperature
  • Check with lube supplier for advice
  • Check for leaking injectors
  • Evaluate equipment use vs. design
  • Evaluate operating conditions
  • Use trained operators
  • Change oil and filters
  • Check for loose fuel crossover lines
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Water/Coolant Contamination

The presence of water in engines indicates contamination from outside sources, from condensation of moisture in the atmosphere, or from internal coolant leaks. Water is typically evaporated by engines at normal operating temperatures. However, water may remain in the oil when engine temperatures are too low for evaporation to occur. Other types of equipment, when operated at sufficient temperatures, also tend to evaporate contaminating water.

Oil analysis offers an effective method of recognizing water/coolant contamination before a major problem occurs. Infrared analysis is used to determine water content in used oil. Results are reported in percent volume. The Karl Fischer method is used to measure water in systems that are sensitive to low moisture content. Karl Fischer results are reported in parts per million (ppm).


Cause
  • Low operating temperature
  • Defective seals
  • New oil contamination
  • Coolant leak
  • Improper storage
  • Cracked Cylinder head
  • Weather/moisture
  • Product of combustion
  • Oil cooler leak
Effect
  • Engine failure
  • High viscosity
  • Poor lubrication
  • Corrosion
  • Engine overheating
  • Acid formation
  • Reduced additive effectiveness
Solution
  • Inspect for cracked cylinder head
  • Inspect heat exchanger and oil coolers
  • Evaluate operating conditions
  • Evaluate equipment use vs. design
  • Avoid intermittent use
  • Check for external water/moisture sources
  • Change oil filter
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Fuel Dilution
Fuel dilution of crankcase oil by unburned fuel reduces lubricant effectiveness. The thinning of the lubricant can lead to decreased lube film strength adding to the risk of abnormal wear. Depending on certain variables, when fuel dilution of crankcase oil exceeds 2.5 to 5 percent, corrective action should be taken. Fuel dilution is measured by gas chromatography. The results are reported in percent volume.

Cause
  • Incorrect air/fuel ratio
  • Extended idling
  • Stop and go driving
  • Defective injectors
  • Incomplete combustion
  • Incorrect timing
Effect
  • Metal-to-metal contact
  • Poor lubrication; oil thinning
  • Increased overall wear
  • Piston ring wear
  • Decreased additive effectiveness
  • Risk of fire or explosion
  • Reduced fuel economy
  • Decreased oil pressure
  • Reduced engine performance
  • High operating cost
  • Shortened engine life
Solution
  • Check fuel lines, leaking injectors or seals, pumps
  • Analyze driving/operating conditions
  • Check spark timing
  • Avoid prolonged idling
  • Change oil and filter more frequently
  • Evaluate equipment and use vs. design
  • Check fuel quality
  • Repair/replace worn parts
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Solids

Solids represent a measurement of all solid and solid-like constituents in the lubricant. The makeup of solids depends on the system. In diesel engines, fuel soot is usually the major constituent measured. In non-diesel components, wear debris and oil oxidation products are measured. All solid material is measured and reported as a percentage of sample volume or weight.


Cause
  • Extended oil drain interval
  • Environmental debris
  • Wear debris
  • Oxidation byproducts
  • Filter leaking or dirty
  • Fuel soot
Effect
  • Shorter engine life
  • Filter plugging
  • Poor lubrication
  • Engine deposits
  • Sludge formation
  • Accelerated wear
  • Decreased oil flow
  • Lacquer buildup
Solution
  • Drain oil, flush system
  • Eliminate source of environmental debris
  • Evaluate equipment use vs. design
  • Evaluate operating conditions
  • Reduce oil drain intervals
  • Change filter
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Fuel Soot
Fuel soot is composed of carbon and is always found in diesel engine oil. Laboratory testing is used to determine the quantity of fuel soot in used oil samples. Stringent exhaust emission regulations have placed greater emphasis on fuel soot levels. One of the most significant impacts of reduced emissions is control of particulate emissions, which resulted in greater soot levels in the crankcase. The fuel soot level is a good indicator of engine combustion efficiency and should be monitored on a regular basis for possible maintenance action.

Cause
  • Improper air/fuel ratio
  • Improper injector spray pattern
  • Poor quality fuel
  • Incomplete combustion
  • Clogged air induction
  • Defective injectors
  • Improper equipment operation
  • Low compression
  • Worn piston/rings
Effect
  • Poor engine performance
  • Harmful deposits or sludge
  • Increased wear
  • Shortened oil life
  • Lacquer formation
  • Clogged oil filters
Solution
  • Ensure fuel injectors are working properly
  • Change oil
  • Evaluate oil drain intervals
  • Check compression
  • Avoid excessive idling
  • Check fuel quality
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Oxidation

Lubricating oil in engines and other components combines with available oxygen under certain conditions to form harmful byproducts. Heat, pressure and catalyst materials accelerate the oxidation process. Byproducts of oxidation form lacquer deposits, corrode metal parts and thicken oil beyond its ability to lubricate. Most lubricants contain additives that inhibit or retard the oxidation process.

Differential infrared analysis offers the only direct means of measuring the level of oxidation in oil. Note: A new oil reference is required for accurate measurement of oxidation. Results are reported on an absorbance scale.


Cause
  • Overheating
  • Extended oil drain interval
  • Improper oil type/inhibitor additives
  • Combustion byproducts/blow-by
Effect
  • Shortened equipment life
  • Lacquer deposits and engine sludge
  • Oil filter plugging
  • Increased oil viscosity
  • Corrosion of metal parts
  • Increased operating costs
  • Increased overall wear
  • Decreased engine performance
Solution
  • Use oil with oxidation inhibitor additives
  • Shorten oil drain intervals
  • Check operating temperature
  • Evaluate equipment use vs. design
  • Evaluate operating conditions
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Nitration
Nitration products are formed during the fuel combustion process when combustion byproducts enter the engine oil during normal operation or as a result of abnormal blow-by past the compression rings. These products, which are more common in oils used to lubricate natural gas- and propane- fueled engines, are highly acidic and create deposits and accelerate oil oxidation. Infrared analysis represents the only method of accurately measuring nitration products in oil. Results are reported on an absorbance scale.

Cause
  • Improper crankcase scavenge
  • Low operating temperature
  • Defective seals
  • Improper air/fuel ratio
  • Abnormal blow-by
Effect
  • Nitrous oxides introduced into environment
  • Acidic byproducts formed
  • Increased cylinder and valve train wear
  • Oil thickening
  • Combustion chamber deposits
  • Increased acid number
Solution
  • Increase operating temperature
  • Check crankcase venting hoses and valves
  • Ensure proper air/fuel mixture
  • Perform compression check or cylinder leak-down test
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Total Acid Number (TAN)
The total acid number is the quantity of acid or acid-like constituents in the lubricant. An increase in TAN from that of the new lubricant should be monitored. The TAN of a new oil is not necessarily zero since oil additives can be acidic in nature. Increases in TAN usually indicate lube oxidation or contamination with water or an acidic product. TAN is an indicator of oil serviceability.

Cause
  • High-sulfur fuel
  • Overheating
  • Excessive blow-by
  • Extended oil drain interval
  • Improper oil type
Effect
  • Corrosion of metallic components
  • Promotes oxidation
  • Oil degradation
  • Oil thickening
  • Additive depletion
Solution
  • Shorter oil drain intervals
  • Verify correct oil type in service
  • Check for overheating
  • Check fuel quality
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Total Base Number (TBN)

The total base number is an expression of the amount of alkaline additives in the lubricant that are capable of neutralizing the acid products of combustion.  A new oil starts with the highest TBN it will possess. During the time the lubricant is in service, the TBN decreases as the alkaline additives neutralize acids. TBN is an essential element in the establishment of oil drain intervals since it indicates whether the additives are still capable of providing sufficient engine protection. 


Cause
  • High-sulfur fuel
  • Overheating
  • Extended oil drain interval
  • Improper oil type
Effect
  • Increased acid number
  • Oil degradation
  • Increased wear
  • Corrosion of metal parts
  • Acid buildup in oil
Solution
  • Use low-sulfur fuel
  • Follow manufacturer's recommendations for oil drain interval, and decrease if engine is operated under severe conditions
  • Verify TBN of new product and use correct oil type
  • Change oil or top off with fresh oil
  • Test fuel quality
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Particle Count
Fluid cleanliness is critical in hydraulic and other systems where high fluid pressure and velocity are involved. Excessive fluid particulate contamination is a major cause of failure of hydraulic pumps, motors, valves, pressure regulators and fluid controls. Failure due to excessive particulate contamination is normally segregated into three areas:
  • Performance degradation
  • Intermittent failure
  • Catastrophic failure
Particle count measurements allow the user to monitor hydraulic system contamination levels on a scheduled basis. Scheduled analysis of hydraulic fluid to include particle count is recommended by most equipment and hydraulic component manufacturers.

Cause
  • Water contamination
  • Machining burrs
  • Filling techniques
  • Oil oxidation
  • Contaminated new oil
  • Worn wiper seals
  • System generated debris
  • Built in contamination
  • Defective breather
Effect
  • Performance degradation
  • Intermittent failure
  • Wear
  • Plugging
  • Leakage
  • Pressure overshoot
  • Momentary hesitation
  • System failure
Solution
  • Filter new oil
  • Change hydraulic fluid
  • Inspect/replace filters
  • Check particle sizes
  • System flushing at high pressure
  • Check air breather
  • Evaluate equipment vs. design
  • Evaluate operating conditions
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Wear Metal/Elemental Analysis

Elemental analysis is used to evaluate and quantify wear metal elements, additive elements and contamination elements. Wear metals are analyzed to pinpoint problem areas through trend analysis. By analyzing the additive elements, the oil type can be verified, i.e., hydraulic oil, transmission fluid or engine oil. Contamination elements are reviewed to determine lubricant serviceability and to pinpoint causes of problems indicated by other test results.

Following are the sources of the elements analyzed and their function in a component:

Wear Metals
Element Source Function
Iron (Fe) Engine blocks, gears, rings, bearings, cylinder walls, cylinder heads, rust Because of its strength, iron is the base metal of steel in many parts of the engine. Since iron will rust, it is alloyed with other metals (i.e., Cr, Al, Ni) making steel.
Chromium (Cr) Shafts, rings, chromate from cooling system Because of its strength and hardness, chromium is used to plate rings and shafts that are usually mated with steel (softer). Chromium is also alloyed with iron (steel) for strength.
Aluminum (Al) Bushings, some bearings, pistons, turbocharger, compressor wheels Aluminum is a strong light-weight metal (smaller mass) that dissipates heat well and aids in heat transfer.
Copper (Cu) Bearings, bushings, oil coolers, radiators Copper is utilized to wear first in order to protect other components. Copper conforms well so it is used to seat bearings to the crankshaft.
Lead (Pb) Bearing overlay, leaded gasoline contamination Lead is a conforming material used to plate bearings. Lead will appear in new engines while the bearings are melding and conforming. If lead appears later, misalignment may be indicated.
Nickel (Ni) Valve stems, valve guides, ring Inserts on pistons Nickel is alloyed with iron in high strength steel used to make valve stems and guides.
Silver (Ag) Bearing cages (anti-friction bearings), Silver Solder, turbocharger bearings and wrist pin bushings Silver is used to plate some components because it conforms well, dissipates heat and reduces coefficient of friction.
Tin (Sn) Bearings, pistons Tin is a conforming material used to plate and protect surfaces to facilitate break-in.
Molybdenum (Mo) Piston rings, oil additives Molybdenum is used as an alloy in some piston rings in the place of Chromium. Molybdenum is also used as a friction-reducing additive in some oils. Soluble Mo can be used as an antioxidant additive.

Additive Elements
Terms
Detergent-additive, which keeps the engine clean at high operating temperature.
Dispersant-additive, which keeps debris in suspension in the oil and controls deposits at moderate temperature.
Anti-wear (AW) additive, which provides a protective film.
Extreme Pressure (EP) additive, which provides a protective film in high-pressure areas.
Element Function
Zinc (Zn) AW, EP, Antioxidant
Phosphorus (P) AW, EP, Antioxidant
Phosphorus is added to extreme pressure oils to provide a protective film. EP oils are characterized by high phosphorus and sulfur levels.
Barium (Ba) Detergent
Barium is toxic and expensive, but it is advantageous because it does not leave excessive ash residue.
Sodium (Na), Calcium (Ca) and Magnesium (Mg) Alkaline (base) additives used to neutralize acids formed by products of combustion in engine oils. They also have some detergent qualities and corrosion inhibition.
Boron (B) Inhibitor
Boron is also found as an additive in coolant as borate.
Copper (Cu) Antioxidant
Copper is added to engine oils to prevent oxidation.


Contaminant Elements
Element Cause
Sodium (Na) External contamination, coolant leak or salt in the air.
Silicon (Si) External (dirt), additive, sealants
Silicon can be an antifoam additive and from gasket material in the form of silicone.
Potassium (K) Coolant leak
Potassium is a coolant additive, and its presence in oil is indicative of coolant contamination.


Quality Equipment Oil Analysis Program
Industry Machine Type Recommended Sampling Frequency

Off Highway and Ground

Diesel engines 150 hours, 10,000 miles
Transportation Gasoline engines 3,000 to 5,000 miles
Mining, construction, Transmissions 300 hours, 20,000 miles
agriculture, bus lines, Gears, differentials 300 hours, 20,000 miles
railroads, forestry, Final drives
automobiles Hydraulics 300 hours, 20,000 miles
 

Aviation Reciprocating engines 25 to 50 hours
Turbines 100 hours
Gearboxes 100 to 200 hours
Hydraulics 100 to 200 hours
 

  
Industrial and Marine Normal Use Intermittent Use
Manufacturing, processing, Diesel engines Monthly, 500 hours Quarterly
power generation, natural gas Natural gas engines Monthly, 500 hours Quarterly
distribution, oil and gas Gas turbines Monthly, 500 hours Quarterly
exploration, marine equipment Steam turbines Bimonthly Quarterly
Air, gas compressors Monthly, 500 hours Quarterly
Refrigeration compressors Beginning, midpoint and end of season
Gears, bearings Bimonthly Quarterly
Hydraulics Bimonthly Quarterly
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Oil Sampling Methods

To properly evaluate machine conditions, the oil samples submitted for analysis must be representative of the system from which they are taken. For best results, follow these guidelines:
  1. The machine being sampled should be brought to normal operating temperature. Oil should be recirculated, if appropriate. This will ensure that insoluable and semisoluable contaminants are uniformly dispersed throughout the system. Samples taken from machines that have been inactive for long periods are not representative.
  2. Oil samples should always be taken in the same manner and from the same sampling point.
  3. Do not sample a machine immediately after an oil change or after a large amount of makeup oil has been added.
  4. Use a clean dry container to draw the oil sample. Ship samples in the plastic bottles provided in the package. Hydraulic fluids or other oils submitted for a particle count analysis should be submitted in the super clean bottles, which are provided when special testing is requested.

Sample Gun Method

The oil test package includes a plastic sampling bottle used for collecting and shipping samples. A special inexpensive sampling gun is also offered as an option, together with convenient lengths of plastic sampling tubing. The plastic sampling bottle fits directly into the sampling gun, and the oil sample can be drawn directly from the machine into the sampling bottle. The sampling gun allows the user to draw representative samples quickly and with a minimum of effort. Procedures are as follows:
  1. Measure a sufficient length of plastic sampling tubing to reach from the sampling gun through the sample aperture and into the machine sump or reservoir. If the machine has a dipstick, the tubing should be measured against the dipstick to establish the proper sampling depth.
  2. Loosen the nut on the sample gun head, insert the free end of the sampling tubing through the nut (about 1/2 inch past nut) and tighten the nut to compress the sealing ring to obtain a vacuum-tight seal. Screw a clean plastic sampling bottle into the gun adaptor.
  3. Holding the sampling gun upright, draw oil into the bottle using the piston lever until oil is within 1/2 inch of the top. To stop the oil flow, break the vacuum by partially unscrewing the bottle. Remove the bottle from the adaptor, screw the cap on tightly and wipe the bottle clean. Fill out the unit or machine identification number on the bottle label.
  4. Replace the plastic tubing after each sampling to avoid sample cross-contamination.

Sample Valve/Petcock Method

Care should be taken to install the valve on the lube system in a location that will ensure representative oil samples can be drawn. The exterior of the valve should be wiped clean prior to sampling to ensure that no external contamination finds its way into the oil. Stagnant oil should be drained from the valve by drawing a small oil sample into a waste oil container just prior to collecting the oil sample in the plastic sampling bottle. Screw the bottle cap on tightly and wipe the bottle clean. Fill out the unit or machine identification number on the bottle label.

Oil Drain Method

Clean the area around the drain plug thoroughly to avoid sample contamination. Allow some of the oil to drain into a waste oil container prior to collecting the oil sample. Place a clean dry sample bottle into the oil stream and fill it to within 1/2 inch of the top. Screw the cap on tightly and wipe the bottle clean. Fill out the unit or machine identification number on the label.

Note: When taking oil samples from hydraulic systems for particle count analysis, special care must be taken to assure the samples are representative and that they are contamination free. Use the special super clean bottles to sample oils for particle count analysis.

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