TM 5-3895-382-24 Scheduled Oil Sampling (S· O·S) Caterpillar  recommends  using  Scheduled  Oil  Sampling (SOS), at regularly scheduled intervals, to complement a good preventive maintenance program. The     Caterpillar     Scheduled     Oil     Sampling     Program, (SOS), was developed to help Caterpillar users realize the   highest   possible   value   from   their   equipment   by minimizing repair costs and maximizing availability.  The SOS   program   is   a   series   of   diagnostic   tests   which analyze    used    lubricating    oils    from    the    oil    wetted compartments of the equipment.  By analyzing the used oils,  problems  may  be  identified  early,  before  extensive component  failure  occurs.   This  reduces  repair  cost  and downtime. The  SOS  program  is  coupled  with  a  wide  range  of repair  options  so  that  when  a  problem  is  identified,  an appropriate matched repair plan is available.  This offers the   user   a   more   complete   service   to   minimize   repair costs    and    schedule    down-time.        S OS    can    also measure   the   effectiveness   of   the   users   maintenance program. Obtain SOS Sample There    are    several    methods    used    to    obtain   SOS samples. NOTE:   Sampling    methods    recommended    are    in preference   order.      If   one   of   the   first   two methods  is  not  feasible,  then  use  the  drain stream method. Use an in-line sampling valve. Use a sampling gun inserted into the sump. Use the drain stream method when changing oil. When  using  the  drain  stream  method  to  obtain  an  oil sample,  take  the  sample  after  some  oil  has  drained  out and before the final drain oil.  The oil at the beginning or end  of  the  drain  stream  is  not  mixed  well  enough  to  be representative  of  circulating  oil  in  the  compartment  and may   carry   debris   that   can   give   false  S OS   analysis results. S· O·S Analysis SOS is composed of three basic tests: Wear Analysis Chemical and Physical Tests Oil Condition Analysis Wear  Analysis  monitors  the  components  wear  rates  by measuring wear elements and contaminants found in the used   oil.      Through   monitoring   the   used   oil,   normal component  wear  trends  are  determined.    Many  failures can be identified when wear trends and/or contaminants significantly exceed past trends. Detectable   failures   are   those   caused   by   component wear  and  gradual  dirt  contamination.    Wear  analysis  is not  able  to  predict  failures  due  to  component  fatigue, sudden loss of lubrication, or sudden ingestion of a large amount   of   dirt   since   failures   of   this   nature   occur   too rapidly. Chemical   and   Physical   Tests   are   used   to   determine whether  the  used  oil  has  been  contaminated  with  water, fuel   or   antifreeze   and   if   these   contaminants   exceed maximum limits. Oil     Condition     Analysis     determines     the     degree     of deterioration of the used oil by measuring the amount of sulfur  products,  oxidation,  nitration  and  soot  present  in the  used  oil.    It  also  can  monitor  additive  depletion  and detect   ethylene   glycol,   Dowtherm   and   butyl   cellosolve contamination. Oil    Condition    Analysis    can    help    regulate    (reduce, maintain  or  extend),  oil  change  intervals  for  a  specific machine/engine   in   a   given   application.      Oil   Condition Analysis  must  always  be  used  with  Wear  Analysis  and the Chemical and Physical Tests. S-O-S INTERVAL CHART Compartment Interval Engine Oil 250 Hours Transmission Oil 500 Hours Hydraulic Oil 500 Hours Final Drive Oil 500 Hours Consult  your  Caterpillar  dealer  for  complete  information and assistance in establishing a Scheduled Oil Sampling Program for your equipment. Maintenance Section Scheduled Oil Sampling (S· O·S) 1-35