Should I use oil content reports?
There are a number of considerations associated with taking an oil sample as well as preparing the report, and there are a number of mechanical considerations associated with estimating engine reliability. RAM reminds aircraft operators that one report, especially one deviation from normal report, is not necessarily sufficient reason to become alarmed.
Certain parts of both Continental ( CMI ) and Lycoming engines, such as rocker shafts and piston rings, typically wear and deposit small quantities of normal wear particles in the oil.
It is a function of engine design.
The Oil Content Report Sample:
The quality of the oil sample has a great deal to do with the report. The individual taking the oil sample should use caution not to take the first oil out of the drain, because the majority of the wear metals could have settled to the bottom of the oil pan. Such a procedure could result in an erroneous reading of the metal concentration.
In addition, oil samples should only be taken from hot oil. Preferred engine warm-up should be done slowly, beginning at idle rpm for a brief period limiting idle to 1200 rpm. If a dip tube is used, it must not make contact with the bottom of the oil pan where concentrations of wear metals are likely to be exaggerated. RAM recommends engine pre-heat when the OAT is below 40°F.
How much is too much?
What is considered a high concentration of wear metal particles? Remember, an oil content report is measured in parts per million ( ppm ). Imagine a large truck filled with 1,000,000 baseballs. If 20 are flawed, they represent 20 ppm. Many engines have remained in service through TBO, even though they had one or more abnormal metal particle reports.
Recently overhauled engines:
Recently overhauled engines may have higher than normal metal particle reports; however, most laboratories are aware of these situations and usually make appropriate adjustments to their reports when so advised of the recent overhaul.