CAUTION Do not add cold water to a hot engine when it  is  not  running. Rapid   cooling   of   an overheated engine will cause severe damage to the   cylinder   head   and   block.   To   cool   an overheated  engine  down,  leave  the  engine running and add water slowly. Watch for the steam that may be produced when adding water. Should a radiator hose burst, secure the engine before  the  temperature  gets  too  high. Oil Pressure Gauge The oil pressure indicator is one of, if not, the most important  gauges  to  watch.  Every  vehicle  or  equipment has an oil pressure warning light or a gauge. Should you start to lose oil pressure and the warning light comes on, secure  the  engine  immediately.  Operating  equipment without proper oil pressure causes severe damage to the engine. Check the oil level in the engine. If the oil level is low, add oil until it is at the proper level. Start the engine; if oil pressure does not register on the gauge or the light stays on for 30 seconds, secure the engine. Then  document  and  report  the  problem. Should the oil level be correct and no pressure registers on the gauge or the warning light stays on, secure  the  engine.  Then  document  and  report  the problem. NOTE: A rule of thumb is that after starting an engine, the oil pressure gauge should show 30 pounds of oil pressure after the engine runs for 30 seconds. Should  the  oil  level  be  correct  but  no  pressure registers  on  the  gauge,  secure  the  engine.  Then document  and  report  the  problem. Air Pressure Gauge There is an air pressure gauge on each vehicle equipped with an air-brake system. The air pressure must be maintained within a range of 100 pounds per square inch (psi) to 120 psi. A warning light or buzzer should come on if the air pressure drops below 60 psi. If there is a rapid loss of air pressure, an air unit may have burst. A slow leak may sometimes be repaired by tightening  a  fitting. WARNING Do not operate any equipment with air brakes if there is an air leak. With  the  engine  at  operating  rpm,  the  air  pressure system  should  build  from  85  to  100  psi  within  45 seconds  in  dual-air  systems.  In  single-air  systems (pre-1975), the pressure should build up from 50 to 90 psi within 3 minutes. Hydraulic Pressure Gauge Most  types  of  construction  equipment  are equipped   with   hydraulic   pressure   guages.   When operating this equipment, you must watch for leaks. Consult  the  operator’s  manual  for  the  pressure  at which  the  equipment  should  be  operated.  Should  the pressure  not  reach  the  operating  range  or  should  you detect a leak, be sure to document and report either or both. Hydraulic  Temperature  Gauge Most  types  of  construction  equipment  are  also equipped with hydraulic temperature gauges. In most cases,   if   the   hydraulic   temperature   exceeds   the recommended  temperature,  it  is  because  the  fluid level is 100 low. Should   the   fluid   level   be   correct   and   the equipment  overheats,  you  are  overworking  the hydraulic  system.   Stop your machine and check the hydraulic   fluid   level. Be  careful  because  the hydraulic fluid is hot and the hydraulic system may be  pressurized.    If the fluid level is normal, let the machine  sit  at  idle  to  cool  the  hydraulics. Fuel Level Gauge When prestart inspecting a piece of equipment, you should visually check the fuel. During the day, watch  the  fuel  gauge  to  ensure  it  shows  a  slow depletion  of  fuel.  Should  the  fuel  gauge  not  move in  a  reasonable  amount  of  time,  assume  the  fuel gauge  is  broken. In  this  case,  check  the  fuel visually from time to time to ensure that you do not run out of fuel. HYDRAULIC  SYSTEMS Hydraulic  systems  on  equipment  are  used  to transmit power for steering and controlling the operation of  mechanical  components.  The  basic  components  of  a 4-7