Oil analysis laboratories tend to provide training that is much more in-depth than what you as an end user would want. Analyzing the data on your own is not easy and can cause you to make a poor decision or pass by a machine that does not have any real issues. It is best to rely on their analysis comments. A major hurdle you face is that a single oil sample report does not really tell you enough solid information about the engine, hydraulic system or transmission. A series of samples over time provides more reliable data. Analysis data should not be taken at face value when you are looking for wear metal trends. On a single report, you get a "number" for iron (Fe). Without having benefit of previous sample history, you do not know if that number is escalating or falling. Just a hard limit is of little consequence. For some engines a silicon (Si) value of 50 PPM could be considered to be possible evidence of dusting (air filter problem) while another engine manufacturer considers an Si number of 7 PPM to be the tipping point. I know of such an engine make (not found in tractors but in mining trucks). Engine companies do not as a rule publish wear metal limits.
More obvious data that may be of help is a report of antifreeze content or fuel dilution. However, you seldom find any sample report that shows antifreeze content as the oil temperatures are high enough to boil off the coolant and water. Unless you know what to look for in the trace elements can you see coolant in the lube oil as a problem. Specifically, look for presence of sodium and potassium as they are found in coolant chemistry. Some coolants use borate buffers. Analysis would show a coolant leak as higher boron. But boron is an additive element. Sample results may not show fuel dilution depending on the initial test method. Some labs use a Seta Flash test. A sample of the oil is heated in a shallow dish. As the lube heats up any fuel in it will vaporize. A flame is introduced above the sample. If it flashes, it is an indication of some threshold percentage of fuel, around 5%. What about a 3% dilution? Much more expensive analysis is needed to accurately detect that. I doubt that anybody selling a machine like that would invest in a sample that may prevent the sale. Basic analysis provides wear metals, glycol test, fuel dilution test, additive metals and elements. What you need is a test for used oil viscosity at 100C and TBN, oxidation and nitration. These are tests for the oil quality and how the engine lubricant has been treated. Bad sample reports can be easily doctored by testing a lubricant that has very low hours of run time. The results will be better for certain while not representing the truth. A series of samples is a better deal by far.
Let's take a different tack on this matter of purchasing a used excavator of any serious investment in a machine. You will pay more for a used machine that you buy from a local equipment distributor. You have a better chance finding oil analysis history from the previous owner. It is in the interest of the seller to have this data. If they do not have it, keep looking. Buying from an established dealer is safer in that his reputation is at stake if he sells a machine that ready for major repairs but is not sold like it is. Somebody selling a machine over the Internet has no real concern about that. Equipment sold at auctions may have some of that backing but you pay more. If you are looking for a bargain, there are no good deals that a simple report will protect you from getting stung. I have 15 years experience with two Caterpillar dealers in the service industry. On more than one occasion we had customers who bought machines at auctions or from a non-local sale. They were stung big time. One of them bought a track loader that had complete junk in the transmission and steering clutches. The final drives were also trash. Still, the tractor would pull it self around. Ran well enough to unload it from the lowboy trailer. The ensuing lawsuit did little for the new owner but to make him wiser. There are no bargains worth pursuing.
As for more information about oil analysis check this site out for more resources:
Oil analysis - Wikipedia, the free encyclopedia
