Piper Navajo PA-31 Service Manual page 513

8-74. RECOMMENDATIONS FOR CHANGING OIL. (Refer to the latest revision of
Lycoming Service Instruction No. 1014.)
a. In engines that have been operating on straight mineral oil for several hundred hours,
a change to additive oil should be made with a degree of caution, since the cleaning action
of some additive oils will tend to loosen sludge deposits and cause plugged oil passages.
When an engine has been operating on straight mineral oil and is known to be in excessively
dirty condition, the switch to additive or compounded oil should be deferred until after the
engine is overhauled.
b. When changing from straight mineral oil to compounded oil, the following
precautionary steps should be taken:
1. Do not add additive oil to straight mineral oil. Drain the straight mineral oil
from the engine and fill with additive oil.
2. Do not operate the engine longer than five hours before the first oil change.
3. Check all oil screens for evidence of sludge or plugging. Change oil every ten
hours if sludge conditions are evident. Resume normal oil drain periods after sludge
conditions improve.
8-75. SPECTROMETRIC OIL ANALYSIS. The use of Spectrometric oil analysis is
becoming widespread in the general aviation field. It is another useful procedure in the
maintenance of modern reciprocating aircraft engines. The spectrometric method requires
complete understanding of the procedures, schedules and interpretation by the maintenance
personnel using this system. It must be remembered that the oil analysis technique is not a
replacement for other established maintenance checks, such as differential cylinder pressure
checks, boroscopic examination, and filter content inspection. The oil analysis is used to
estimate wear ratio values of the particular engine or engines being monitored. For further
information on Spectrometric oil analysis, refer to the latest revision of Lycoming Service
Letter No. L171.
Revised:
9/2/81
POWER
PLANT
Revised: 9/24/81
POWER
PLANT
PIPER NAVAJO SERVICE MANUAL
2J15