TM 10-3930-671-24 maintenance when authorized by unit maintenance. g. Oil Filter Statement.  Oil filters shall be changed as applicable, when: (1) They are known to be contaminated or clogged. (2) Service is recommended by AOAP laboratory analysis. (3) At prescribed hard-time intervals. h. AOAP Sampling Interval Statement.  Engine oil must be sampled at 50 hours of operation or 90 days, whichever occurs first, for Active Army Units.  Reserve and National Guard activities will use 50 hours or 180 days, whichever occurs first, as the prescribed interval.  Hydraulic fluid will be sampled once a year. Sampling will be performed as prescribed by DA Pam 738-750. l. Warranty  Hard-Time  Statement.    For  equipment  under  manufacturer’s  warranty,  hard-time  oil  service  intervals shall be followed.  Intervals shall be shortened if lubricants are known to be contaminated or if operation is under adverse conditions such as longer-than-usual operating hours, extended idling periods, or extreme dust. j. Lubrication Interval Symbols.  The following lubrication interval symbol is used: H - Hours (operated) k. Lubrication Figure Explanation.  The following lubrication instructions include Figures E-1 through E-3.  Figure E-1 identifies locations of grease fittings.  Figure E-2 identifies components with fluids and/or filters to be serviced/checked at  short-term  intervals.    Figure  E-3  identifies  components  with  fluids  and/or  filters  to  be  serviced/replaced  at  long-term intervals.    All  figures  identify  component,  level  required  to  perform  maintenance,  time  interval  to  perform  maintenance, lubricant used, and component capacity, if applicable. I. General Engine Oil Checks and Services. (1) Oil grade requirements are listed on the Lubrication Figures (Figures E-1 through E-3). Hot  engine  oil  can  cause  severe  burns  and  personal  injury.    Care  should  be  exercised  when changing oil filter and draining hot oil. (2) Park truck on level ground and allow it to sit about ten minutes before checking oil level.  Parking on level ground provides the most accurate level reading on the dipstick.  Waiting ten minutes, before checking oil level, allows all oil to drain into crankcase. (3) Before changing the engine oil, the engine should run for a few minutes to heat the oil.  Warm oil will flow more easily and help to drain all oil sludge from the crankcase. Do not overfill crankcase with engine oil, or serious damage may occur to engine. (4) Do not overfill crankcase. (5) Ensure oil level is correct before operating the truck. E-2