There is no substitute for machinery component oil analysis on a timely and constant basis. None! If you only sample infrequently or for a limited period of time, you have to accept the risk that you will miss a major and costly failure.
As salesrep explains, you are mainly looking for trends in the amount of different wear metals, but also silicon (dirt), water (including glycol), fuel, and additive package minerals or chemicals. Wear metals go up with increased time on oil, additives come down with depletion. Too much fuel, glycol, water, and silicon is bad. You must have several oil sample reports to start a trend and see where your oil is going and what's happening to it in your machine. For instance, I can tell, with a decent sample trend, if a particular brand of oil has been switched for another.
You can compare similar machine oil samples in your own fleet, or those of similar machines in other folks fleets. This helps you see what all machines of that type or manufacturer are doing and whether yours is outside the norm. Be careful however, results can vary wildly for a number of reasons.
However, and an important point missed by many people, is you are trying to see a potential catastrophic event before it happens. There may be other physical indications that such an event is about to happen, but a fluid sample will likely alert you in time to make it a minor repairable situation, instead of a major issue causing a job shut down and potential loss of work for many people.
Remember too, that the limits manufacturers people post are averages for a wide range of machines in a huge number of situations. Your own results need to be studied carefully to see how the units are acting in your operations. You may have certain unique situations that your machines have to cope with that may increase or decrease readings.
Generally speaking, you want metals to be as low as possible, but even new oils have some, so a new oil sample is a must so that you have a baseline to start with. Silicon levels more than 10 are bad, indicating that you have dirt coming into the compartment. However, some hydraulic oils have silicon as an additive to help prevent foaming, a base sample will identify that. Water and glycol are always no-no's. Nearly any amount is bad. Fuel in any amount is bad though there is nearly always a trace. Total base number is important as it tells you, in part, how your additive package is doing, not all oils show as high as the producer claims they will. The numbers for some of the additive ingredients will tell the rest of the story. Older components tend to use up additives faster than new. There is much more that I do not have time to list.
Wulf listed excellent reading material. Some of the stuff presented in the two examples is for real egg-heads, but they also have fairly readable and understandable articles that point out much valuable information for the construction machinery end-user. He is also correct that most lab reps will love to present you with more information than you can digest at one or more sittings. You can also get excellent analysis information from most equipment dealerships if you press hard enough.
Oil analysis will save you money in the long run if you stick to it faithfully. It only takes one or two severe failures to pay for a year or more analysis.
Good Luck!
