TM 5-3895-382-24 Caterpillar's  20  times  rule  for  TBN  (Reference:  Oil  and Your   Engine,   SEBD0640)   versus   fuel   sulfur   was   a general  requirement  developed  in  the  early  1980's  for Caterpillar prechamber combustion (PC) system engines.    Caterpillar  still  maintains  20  times  TBN  value for PC engines.  Engines built prior to 1990 can continue to   use   single   grade   viscosity   oil   or   commercial   oils, provided the engine operates satisfactorily. Fuel sulfur neutralization of new oil formulations in direct injection  (DI)  system  engines  is  more  effective.    Field results   indicate   that   direct   injection   (DI)   combustion systems   and   the   oils   now   recommended   for   those engines will operate at an oil TBN equal to ten times the fuel sulfur. Caterpillar Direct Injection Diesel Engines For  direct  injection  engines  running  on  distillate  diesel fuel, the minimum new oil TBN (by ASTM D 2896) must be  10  times  the  fuel  sulfur  level,  and  the  minimum  TBN is   5   regardless   of   low   fuel   sulfur   level.      See   the illustration. Oil TBN shown by ASTM D2896 (Y).  Percent of fuel sulfur by weight (X).  New oil TBN (1).  Change oil when the used oil TBN limit (2) is reached. In   areas   where   the   fuel   sulfur   exceeds   1.5   percent, choose an oil with the highest TBN that is within the API CF-4  or  CG-4  categories,  and  shorten  the  oil  change period  based  on  oil  analysis.    The  oil  analysis  should evaluate  oil  condition  and  wear  metals.    High  TBN  oils that are not within the API CF-4 or CG-4 categories can produce excessive piston deposits leading to a loss of oil control and bore polishing. NOTICE Operation  at  fuel  sulfur  levels  over  1.5  percent  may require   shortened   oil   change   periods   to   maintain adequate wear protection. Engine Lubricant Viscosity Recommendations The proper SAE viscosity grade oil is determined by the minimum  outside  temperature  at  cold  engine  start-up, and   the   maximum   outside   temperature   during   engine operation.  Use the minimum temperature column in the lubricant   viscosities   chart   determine   the   oil   viscosity required   for   starting   a   cold   soaked   engine.      Use   the maximum temperature column in the lubricant viscosities chart  to  select  the  viscosity  for  operation  at  the  highest temperature   anticipated.      In   general,   use   the   highest viscosity    oil    available    that    still    meets    the    startup temperature requirements. PROTECTION OF SEVERAL ENGINE OIL VISCOSITIES Ambient Temperature Engine Oil Viscosity Grade Minimum Maximum SAE 0W-20 -40C (-40F) 10C (50F) SAE 5W-30 -30C (-22F) 30C (86F) SAE 5W-40 -30C (-22F) 40C (104F) SAE 10W-30 -20C (-4F) 40C (104F) SAE 15W-40 -15C (5F) 50C (122F) Maintenance Section Lubricant Specifications 1-38