Hydrometer A hydrometer is the instrument used to measure the amount of active ingredients in the electrolyte of the battery.  The  hydrometer  measures  the  SPECIFIC GRAVITY of the electrolyte. Specific gravity is the ratio of the weight of the electrolyte to the weight of the same  volume  of  pure  water,  The  active  ingredient,  such as sulfuric acid or potassium hydroxide, is heavier than water.  Because  the  active  ingredient  is  heavier  than water, the more active the ingredient in the electrolyte, the heavier the electrolyte will be; the heavier the electrolyte, the higher the specific gravity. A hydrometer is a glass syringe with a float inside it. The float is in a hollow, glass tube, weighted at one end and sealed at both ends, with a scale calibrated in specific gravity marked on the side. The electrolyte to be tested is drawn into the hydrometer by the suction bulb. Enough electrolyte should be drawn into the hydrometer so that the float will rise. Hydrometers should not be filled to the extent that the float rises into the suction bulb. Since the weight of the float is at its base, the float will rise to a point determined by the weight of the electrolyte. If the electrolyte contains a large concentration of the active ingredient, the float will rise higher than if the electrolyte has a small concentration of the active ingredient. To read the hydrometer, hold it in a vertical position and take the reading at the level of the electrolyte.  Refer to the manufacturer’s technical manual for battery specifications to find the correct specific gravity ranges. An example of what your manual may say about the specific gravity is that for a fully charged battery the specific gravity should be 1.280 ± 0.005. The manual may tell you to recharge the battery if the specific gravity is less than 1.250. Always return the electrolyte in the hydrometer to the cell of the battery from which it was taken. NOTE: Hydrometers should be flushed with fresh water  after  each  use  to  prevent  inaccurate  readings. Storage battery hydrometers must not be used for any other  purpose. Perhaps  it  should  be  said  that  adding  the  active ingredient  (sulfuric  acid,  for  example)  to  the  electrolyte of a discharged battery does not recharge the battery. Adding  the  active  ingredient  only  increases  the  specific gravity of the electrolyte and does not convert the plates back to active material, and so does not bring the battery back to a charged condition. A charging current must be passed through the battery to recharge it. Oil You must check the engine crankcase oil level before operating the generator set. The engine dipstick (fig. 3-1, view B) is the crankcase oil level gauge. The dipstick in the generator engine is the shielded type, which allows checking the oil level while the engine is either stopped or running. The dipstick is stamped on both sides to indicate the two different oil levels. The engine  running  side  is  stamped  as  follows:  "ADD," "FULL," and "RUNNING." The engine stopped side is stamped   as   follows: "ADD,"    "FULL,"   and "STOPPED." Be sure to use the appropriate add and full marks, depending on whether the engine is stopped or running. Also, ensure that the appropriate side of the dipstick is up when inserting it since the underside will be  wiped  in  the  gauge  tube  when  the  dipstick  is removed, therefore, indicating a false oil level reading. To check the oil level, first remove and wipe the oil from the dipstick. Loosen and remove the oil filler cap (fig. 3-1) to allow the pressure to escape. Reinsert the dipstick (with the appropriate side up) and remove it to observe the oil level. Add oil through the fill tube, as required, to obtain the "full" level on the dipstick. Be sure to use the proper grade of oil.   A lubricant chart in the  instruction  manual  furnished  with  each  generator will show the proper grade of oil to use at the operating temperature. Water Check that the level of coolant is within 2 inches (51 mm) of the top of the radiator. WARNING Do not attempt to remove the radiator cap until the radiator has cooled to a point where there  will  be  no  built-up  steam  pressure. Failure to observe this warning could result in second- or third-degree bums. 3-6