Originally Posted By: Snagglefoot
In our discussions on UOA results it’s been said you can’t compare numbers if you are talking about different engines. Also, there are wear numbers all over the place. I try normalize numbers by looking at iron wear as PPM per thousand miles. Seems to me 1 is good and 3 is bad, again ignoring engine differences.
Has anyone tried getting UOA’s with one oil, changing to a different oil and then getting consistently better or worse UOA’s?
Also, would you feel like changing what you use if you had 3 PPM per thousand miles like some of the UOA’s out there?
Thanks for your ideas.
UOA's are not a tool designed for measuring wear, once you understand that, it makes their use and understanding the results a whole heck of a lot easier.
UOA's are a tool for determining the condition and continued serviceability of the lubricant. They are also useful for exposing potential mechanical problems like coolant ingress, air intake tract leaks, fuel dilution and failing mechanical parts (if the failure rate is slow enough). Each lubricant and equipment combo will have a "wear signature" that, when trended, can be used to fine tune the safe usable life of the lubricant as well as allow for the spotting of anomalies which can point to some of the issues mentioned earlier. You cannot reliably trend using different lubricants and you cannot compare metal uptake rates, within reason*, between different lubricants to determine which one is "better". This is due to the very small range of particle sizes that UOA's sample and the fact that you are inferring mechanical wear based on particles that may not be exclusively from that process. Chemical chelation, corrosion and the like can also be a source of these particles, but there is no way to differentiate the sources.
Iron is a metal that follows engine hours. This means that in most equipment posted on BITOG, it follows mileage, albeit indirectly. Other metals do not present in that manner. Aluminum, copper, lead...etc should all be at very low levels (generally) and spikes in these can indicate issues. They can also be benign however, like copper can be chelated from an oil cooler, artificially increasing its number, lead can be from using leaded race fuel...etc.
Significant changes in trended wear rates then should warrant investigation. However, most serious mechanical failures will happen rapidly enough that you'll never spot them in a UOA. This is generally the case for rapid deterioration of mechanical components and is supported by numerous experiences on this board, like former user BuickGN who was taking out rod bearings, yet seeing good UOA's.
*If oil "A" results in consistently trended higher levels of metals than oil "B", then oil "B" could likely be concluded to be the better choice if the metal is aluminum, lead or copper, as these should, generally, always be at low levels. Iron needs to be viewed through the lens of PPM/1K miles or PPM/time and thus,
significant trended deviation here would need to be the case before making the same conclusion. 12ppm in 5,000 miles vs 20ppm in 7,000 miles; 2.4ppm/1K miles vs 2.8ppm/1k miles for example, is nowhere near significant.