What is a Used Oil Analysis (UOA), and where/how/why is it done?
It is an analysis of used engine oil performed at a lab. Customers collect some of their used oil, usually during the oil change, and send it in to the lab to be analyzed. Two of the most popular testing labs are:
http://www.blackstone-labs.com/http://www.dysonanalysis.com/index.htmlAfter running several tests on the oil sample sent to them, the lab sends the customer a data sheet which reveals the condition of the oil and any problems occurring within the engine. The amount of engine wear that took place while using the oil is related to the amount of certain metals found in the used oil. The metals found in the used oil come from engine wear, and an oil that offers good protection will have low numbers of these metal particles in it. A UOA will also show how much the oil sheared down with use, and if it is safe to use it or a longer oil change interval. A Used Oil Analysis also highlights the condition of the engine and identifies any potential problems that may be developing by detecting the presence of any dirt, anti-freeze, sludge or fuel in the oil.
Where are the UOA results posted?
The UOA results are collected in comparison charts attached below. The charts list the average result for each oil tested, including the amount of engine wear that took place using the oil, the oil’s ability to resist shear, and the amount of active additive left in the oil. The individual UOA results are posted throughout this thread as they are submitted by members. Only current formulations of oil are included in the comparison charts attached below.
How do I read the attached UOA Comparison Charts?
The name and weight of each oil tested is at the top of the comparison charts. The column below it shows the average mileage on that particular oil, followed by any amount of make-up oil added during the average oil change interval. This is important to look at when comparing oils, as an oil that has just 1,000 miles on it when tested will obviously fare better than an oil that has 9,000 miles on it when tested, even if it is not really a better performing oil. The next part (The Grey Section) of the column contains the elements found in the used oil, measured in parts per million (ppm). This reflects the type and amount of metals that were worn off of engine parts. Lower levels of metals are better. The bottom of the column (The Red Section) shows the oil viscosity and TBN of the oil after use.
Where exactly do the traces of metals come from, and how do they indicate engine wear?
The most common metals in your used oil and where they come from are listed below. These metals come off of different parts of your engine during operation. Your oil protects the surfaces of your engine from wear, but some oils do a better job of others. Oils that have low numbers of these metals did a good job of protecting the engine’s surfaces from wearing down with use. So look for an oil that shows low numbers of these elements:
Iron: Comes from cylinder liner, camshaft, oil pump, and timing chain wear
Chromium: Comes from piston ring wear
Copper: Comes from bearings, valve guides, and bushings wear
Lead: Comes from bearing wear
Aluminum: Comes from piston and piston thrust bearing wear
Silver & Tin: Comes from bearing wear
Which metals are the most important to have low numbers?
I look for the lowest possible numbers of Lead, Copper, and Chromium in the oil sample to indicate better protection of critical areas. The bearings and piston rings are not just critical areas because of their function, they are critical to protect because they comprise a much smaller amount of the total engine mass than Iron and Aluminum parts. 5ppm wear of Lead off a relatively tiny bearing is a much higher percentage of wear than 5ppm of Iron would be from all the Iron found in the crankshaft, camshafts, timing chain, etc... The same principle applies to the piston rings, where 2ppm of Chromium is considered high wear for such a small part.
Where do the other elements come from, and do they indicate engine wear?
The only other element to look for in low numbers, in addition to the wear metals listed above, is silicon. High silicon could mean a bad air or oil filter is not trapping dirt. The other trace elements are usually part of an additive package that oils use, and are not from engine wear. Looking at the numbers of these other elements can be useful in determining if a manufacturer has changed their formula, or to see what type of additives they use. The most common other elements found in an oil sample and what they commonly indicate are:
Silicon: dirt ingestion, sometimes used as an anti-foamant
Molybdenum: anti-wear additive and friction reducer
Boron: anti-wear additive and friction reducer
Calcium: common additive with many functions, primarily a detergent
Magnesium: common additive with many functions
Phosphorous: anti-wear additive and friction reducer, shear stabilizer
Zinc: anti-wear additive and friction reducer, shear stabilizer
What do the viscosity numbers mean, and how do I read them?
The viscosity numbers are from a specific test to determine the viscosity of an oil at a given temperature, as measured in cSt (centistokes). A higher number means a thicker oil at operating temperature, and a lower number means a thinner oil at operating temperature. A higher or lower number is neither good or bad in and of itself, it is merely a measure of the oil’s viscosity. Some oils thinned out, or sheared, from use and became thinner than their original grade. For example, a used 30wt oil might have viscosity numbers which correlate with a 20wt oil, indicating it is prone to shearing in the VQ.
Are higher or lower TBN numbers better, and why don’t all the oil results have a TBN number?
All engine oils break down with use and time. The result is an accumulation of acids in the oil. These acids are what form sludge. The oil’s base stock and the additives in the oil work together to help prevent sludge from forming. The Total Base Number (TBN) is a measure of how well the formulation is working to fight sludge and acid build-up. A high TBN means there is more base than acid in the used oil. A lower TBN number means more acids formed over time than in an oil with a higher TBN. The TBN of a used oil is a good indication of how robust the oil is for extended oil change intervals, with higher TBN numbers indicating an oil is good for longer oil change intervals. It usually costs extra to get a TBN test done, so not all of the samples have a TBN value.
