I decided to write about understanding UOA's for my chemistry term paper this semester worth 15% of my overall grade, and thought I would share it with you guys to get some input, or just has a good ol' discussion. The only criteria was that it had to deal in some way with chemistry, and we only had to make it 3 pages in length (double spaced) but there wasn't any way I could condense all of the basics of oil into that little space. It ended up at 9 pages including the cover and references sheet.
Keep in mind that this was written between 12am-4am last night while relying on mostly memory and pina colada Sobe drinks, so I know there might be quite a few errors and half-arsing at some points (I was tired). It was also formatted in Microsoft Word so the spacing, sizes, etc will look a little quirky but it looks very professional when printed. Copy and paste onto the forum just doesn't do it justice but I'll try my best.
Any comments/feedback/suggestions/corrections are gladly welcomed because I am for all intents and purposes, a noob at this whole thing and always looking for a chance to learn what I don't know.
Engine Oil Analysis
Understanding Spectral Analysis of Engine
Oil & Its Real-World Application
What is an engine oil analysis?
Engine oil analysis is a process that involves a sample of engine oil, whether virgin or used, and analyzing it for various properties and materials to monitor wear metals and contamination. By analyzing a sample of used engine oil, you are able to determine the wear rate, and overall service condition of an engine, along with spotting potential problems and imminent failure before it happens. This is a critical tool to use in certain industries such as aviation, racing, and commercial shipping fleets where downtime due to engine failure can be costly and potentially dangerous.
How does an engine oil analysis work?
Oil analyses are offered by many companies and are accomplished by using spectrometry. A spectral exam is done by injecting the oil sample into inductive coupled argon plasma, which is around 10,000° Celsius. The light generated from injecting the oil into the plasma is directed through a prism and broken up into different wavelengths and intensities. Those are then collected on an aperture plate, sensed by a photomultiplier tube, and given as a digital readout on the computer’s display. Each element and their concentrations have their own unique wavelength and intensity which can be matched against a calibrated sample to give you an accurate readout of each element and their concentration.
What is a real world application for an engine oil analysis?
By knowing the amount of each elemental metal in the sample, you are able to narrow down and monitor how specific components in an engine such as bearings are wearing. Not only can an analysis detect these trace metals, but they can also detect various types of contamination. Such as insoluble matter, fuel, or coolant, and be able to spot any abnormalities before they become a costly or dangerous problem. This allows industries to increase an engine’s service life, reduce repair bills, unscheduled down time, and catastrophic failures.
Interpreting and understanding an engine oil analysis report:
Below is a report given on a sample of used engine oil which I had analyzed from my personal vehicle, and the source each wear metal generally indicates inside an engine.
**Note: all universal averages are compared to an oil sample which was in use for approximately 4,100 miles in an identical engine, while my sample was in use for 8,740 miles.**
Aluminum - Aluminum is most commonly from wear (scuffing) on piston skirts as they repeatedly travel along the length of a cylinder. Other sources often include aluminum engine blocks, certain types of bearings, and heat exchangers (oil coolers).
Chromium - The source of chromium wear metals are almost always exclusively from piston rings which are used to form a tight seal between the moving piston and stationary cylinder wall. These rings have to reliably create a tight seal between the piston and the cylinder wall while travelling at up to 4,000+ feet per second and dealing with peak pressures of over 2,000 psi (136 Bar) depending on the engine design and usage.
Iron - This is the only wear metal that accurately and linearly increases with the length of time the sample has been in service. It has many sources inside of an engine, most commonly coming from cylinder liners, camshaft lobes, crankshaft journals, and oil pumps.
Copper – Copper is widely used due to its high ductility and thermal conductivity. It is mainly utilized in bushings and bearings such as: crankshaft journal bearings, connecting rod bearings, camshaft bushings, piston wrist pin bushings, thrust washers, and even heat exchangers (oil coolers).
Lead – Lead is a soft, sacrificial wear metal used on surfaces such as bearings. Lead based Babbitt alloys. Commonly found in main crankshaft journal bearings and contaminated fuels. Other sources include leaded fuels and gasoline octane improver.
Tin – Commonly alloyed with Copper and Lead, it is typically found in crankshaft journal, connecting rod, and camshaft bearings, along with heat exchanger cores and thrust washers.
Molybdenum – This is most commonly used as an anti-wear/anti-scuff additive and has an effect commonly called “Moly plating” where over time, a thin and microscopic layer of Molybdenum tends to form between contact surfaces, thereby creating a lower coefficient of friction between the two parts. Concentration levels of Molybdenum vary greatly depending on the formulation of each specific oil brand, and viscosity. Oil brands with high Molybdenum concentrations include Red Line Oil and Royal Purple.
Nickel – Though not very widely used anymore, Nickel can be found in certain alloys of steel for internal engine parts, and also is used as a coating on bearings.
Manganese – Manganese is sometimes used in certain steel alloys and has virtually no other uses in these applications.
Silver – Due to its exceptional thermal conductivity, it is sometimes used as a coating for bearings providing minimal friction. However, it is susceptible to attack from Zinc-based additives and is not commonly used in the U.S. for equipment.
Titanium – Titanium is a newer, more environmentally friendly anti-wear additive being implemented due to more stringent emissions regulations, and is phasing out older, harmful phosphorous compounds such as ZDDP (Zinc dialkyldithiophosphate). ZDDP reduces the effectiveness of the catalysts in catalytic converters by creating a plating effect when combusted, and covering the catalyst. Titanium chemically binds to wear surfaces creating a hard, Titanium based oxide layer which reduces friction, thereby reducing wear. Concentration levels vary greatly depending on oil brand. Oil brands currently high in Titanium concentrations include Castrol Edge with Titanium.
Potassium - Most commonly found if there is a coolant mixing with, and contaminating the engine oil.
Boron – Used as a corrosion inhibiter, anti-wear and anti-oxidant additive. Concentration levels vary greatly depending on oil brand.
Silicon – A very common contaminant most typically found in a very abrasive solid form, which causes increased metal wear numbers (especially Iron) in oil analysis samples. However, in my case it is harmless and leaching from a silicone sealant which I used to seal a leaking valve cover gasket, though the most common source is from insufficient air filtration. Silicon concentrations in such cases as this will typically drop after each subsequent oil change.
Sodium – This is most commonly used as a corrosion inhibiter additive, and occasionally can indicate a coolant leak into the oil. Concentration levels vary greatly depending on oil brand.
Calcium – Used as a detergent and dispersant additive to maintain suspension of particulate matter, along with maintaining a reserve alkalinity. Concentration levels vary greatly depending on oil brand.
Magnesium – Also used as a detergent and dispersant additive to maintain suspension of particulate matter, and occasionally used in certain alloys of steel. Concentration levels vary greatly depending on oil brand.
Phosphorus – Used as an anti-wear, anti-oxidant, extreme pressure, and corrosion inhibitor additive. Concentration levels vary greatly depending on oil brand.
Zinc – Another anti-wear, anti-oxidant, and corrosion inhibitor additive also commonly found in bearing alloys. Concentration levels vary greatly depending on oil brand.
Barium – A detergent which also acts as another corrosion and rust inhibitor. Concentration levels vary greatly depending on oil brand.
SUS Viscosity @ 210°F – The Saybolt Universal Second viscosity (SUS) is a measurement of viscosity that 60 cm3 of oil takes to flow through a calibrated tube at a controlled temperature (210°F in this case). Each weight of oil such as a 30 weight (5w30/10w30/etc) has an acceptable range to fall into to meet that grade. In this case of a used motor oil sample, it should fall between 56 and 63 SUS. It fell at 56.9, which is slightly less viscous than a virgin sample of this identical oil, which began at 58.3 SUS. That means the sample had a 2.4% viscosity loss over its service life due mainly to shearing and slight fuel dilution. Oils such as Castrol Edge 5w30 are on the thinner end of the 30 weight spectrum, and are on the borderline of being a “thick” 20 weight oil straight from the bottle. They don’t take long to fall into that range when they shear.
cSt Viscosity @ 100°C – Viscosity at 100°C given in Centistokes. Less commonly used so there isn’t much to discuss here. Sorry folks.
Flashpoint in °F – This is basically the temperature at which the oil sample will start to combust in °F. Lower flashpoints tend to indicate a presence of fuel. The flashpoint of this sample was 410°F while a virgin sample of this identical oil began at 420°F, so the fuel content of this sample is quite low.
Fuel % - This is the amount of raw fuel content in your oil sample given as a percentage of total volume. Fuel dilution is common from cold starts with lots of idling (engine ECUs typically run rich on a cold idle) and short trips. This causes raw fuel to work past the piston rings and into your crankcase, which dilutes your oil and acts as a solvent, partially washing away the critical oil film and increasing wear between parts. This is why used motor oil (especially on older carbureted vehicles) sometimes smells like gasoline.
Antifreeze % - Percentage of antifreeze found in the sample given as a percentage of total volume. Antifreeze will show up in an oil sample and indicate a coolant leak into the oil from such things as cracked engine blocks or cylinders heads, and leaking cylinder head gaskets.
Water % - Percentage of water found in sample given as a percentage of total volume. Moisture is common in short trip vehicles that don't fully get the oil up to operating temperature long enough. It takes 10-15 minutes for the oil to get up to operating temperature, which is enough to start evaporating the moisture in the sample. The same goes for fuel in your sample too. An occasional long highway drive is good for your oil.
Insolubles % – This is the amount of insoluble material in the sample given as a percentage of total volume. The most common insolubles are carbon from the combustion chamber, and dirt that gets sucked in through the engine’s intake system. This is mostly what turns your oil darker the longer it has been in service. High insoluble percentages indicate insufficient air and oil filtration, with the latter being the most common cause.
TBN - The TBN (Total Base Number) is a lubricant’s reserve alkalinity measured in milligrams of potassium hydroxide per gram of oil. Or in more simple terms, the amount of active additives remaining. This number is important because combustion byproducts tend to form acidic compounds and the TBN is the acid-neutralizing capacity of the lubricant. TBN does not decrease linearly with the time it has been in use. Example: it could start out at a TBN of 10, drop to 5 after only 1,000 miles of use, and then stabilize around 3 for a majority of the remaining service life. A TBN of <1.0 is generally considered to indicate near depletion of additives, and is a safe point to change your oil. Once the additives are depleted then the infamous sludge that the crazy Scot from the Castrol commercials has been warning us about can begin to form. A virgin sample of this identical oil begins with a TBN of 11.7.
TAN – The TAN (Total Acid Number) is the amount of potassium hydroxide measured in milligrams needed to neutralize the acids in one gram of oil. When plotted on a graph with the TBN, the point at which the two lines cross is the optimal point to change your oil and indicates nearing additive depletion. For cost reasons I didn’t get the TAN test done because the TBN is a more reliable method to determine the active additive remaining.
Stark, J. (n.d.). Spectrometry: The Marvel Of The Lab. Retrieved April 6, 2011, from Blackstone Labs: http://www.blackstone-labs.com/spectrometry-the-marvel-of-the-lab.php
What Is Oil Analysis? (n.d.). Retrieved April 6, 2011, from Bob Is The Oil Guy: http://www.bobistheoilguy.com/cms/index.php?option=com_content&view=article&id=50&Itemid=56
Sources Of Wear Metals In Oil Analysis. (n.d.). Retrieved April 6, 2011, from Bently Tribology Services: http://www.bentlytribology.com/publications/appnotes/app31.php