TM 10-3930-659-10 2-30.  OPERATE IN EXTREME HEAT (Con’t). (11)  Severe  heat  increases  pressure  In  closed  pressurized  systems,  such  as  hydraulic  system  and  cooling system,  and  Increases  the  volume  of  liquids.    Ensure  that  working  pressure  Is  within  safety  limits  and  use caution when removing hydraulic fill cap and, if necessary, radiator fill cap. (12) Try to keep forklift truck in shade, or at least partially covered, to lessen heat damage.  Ensure that all window surfaces In cab area are covered. (13)  When  operating  forklift  truck  in  temperatures  above  100°F  (380C),  extra  care  must  be  taken  to  prevent overheating of engine and transmission. Temperatures may be between 10 °F to 20 °F (-12 °C to -7°C) hotter than normal.  Monitor engine coolant high temperature indicator and transmission oil temperature gage.  If the temperatures continue to rise, put forklift truck in neutral and rev up engine to approximately 1200 rpm until indicator goes out and gage drops back to a more normal operating temperature. (14) Operate In lowest gear range allowable for the Job you are doing.  Keep load lifted as low as possible to avoid overloading the forklift. (15) Do not open engine access doors with the engine running to attempt to cool down the engine.  Opening these doors interferes with proper airflow and may Increase heating or damage the engine. b.  Battery Checks. (1) Batteries do not hold their charges well in extreme heat.  Battery specific gravity should be adjusted by Unit Maintenance for the expected temperatures, and ensure that only distilled water is used in batteries. (2) Have Unit Maintenance set the voltage regulator at the appropriate specification for your area. (3) Monitor charging system closely to ensure that batteries are not overcharging or undercharging. (4) Make sure that battery air vents are kept clean. (5) If forklift truck is not to be used for two days, remove batteries and store In a cool place. c.  Cab Operations. (1) Ensure that sufficient air is kept moving by use of defroster fan (see paragraph 2-22). (2)  Operator  fatigue  will  be  greater  during  extreme  heat;  therefore,  frequent  operator  changes  or  rest  periods should be observed. 2-72