Ventilator plug Figure 8-20.  Ignition harness lead support installation. Figure 8-19.  Dehydrator plug “blue” showing low humidity  (Sacramento Sky Ranch).  the engine has so little moisture that internal corrosion is held  to a minimum. This same cobalt-chloride-treated silica gel is  used in humidity indicator envelopes. These envelopes can  be fastened to the stored engine so that they can be inspected  through a small window in the shipping case or metal engine  container. All desiccants are sealed in containers to prevent  their becoming saturated with moisture before they are used.  Care should be taken never to leave the container open or  improperly closed. Before an engine is placed in temporary or indefinite storage,  it should be operated and filled with a corrosion-preventive oil  mixture added in the oil system to retard corrosion by coating  the engine’s internal parts. Drain the normal lubricating oil  from the sump or system and replace with a preservative oil  mixture according to the manufacturer’s instructions. Operate  the engine until normal operating temperatures are obtained  for at least one hour.  Always take the appropriate precautions when turning or  working around a propeller. After the flight, remove all the  spark plug leads and the top spark plugs.  To prevent corrosion, spray each cylinder interior with  corrosion-preventive mixture to prevent moisture and oxygen  from contacting the deposits left by combustion. Spray the  cylinders by inserting the nozzle of the spray gun into each  spark plug hole and playing the gun to cover as much area  as possible. Before spraying, each cylinder to be treated  should be at the bottom center position and the oil at room  temperature. This allows the entire inside of the cylinder  to become coated with corrosion-preventive mixture. After  spraying each engine cylinder at bottom center, respray each  cylinder while the crankshaft is stationary with none of the  cylinder’s pistons at top dead center.  The crankshaft must not be moved after this final spraying,  or the seal of corrosion-preventive mixture between the  pistons and cylinder walls are broken. Air can then enter past  the pistons into the engine. Also, the coating of corrosion- preventive mixture on the cylinder walls is scraped away,  exposing the bare metal to possible corrosion. The engine  should have a sign attached similar to the following: “DO  NOT TURN CRANKSHAFT—ENGINE PRESERVED  PRESERVATION DATE ____________.” When preparing the engine for storage, dehydrator plugs are  screwed into the spark plug opening of each cylinder. If the  engine is to be stored in a wooden shipping case, the ignition  harness leads are attached to the dehydrator plugs with lead  supports.  [Figure 8-20]  Special ventilatory plugs are installed  in the spark plug holes of an engine stored horizontally in  a storage container. Any engine being prepared for storage  must receive thorough treatment around the exhaust ports.  Because the residue of exhaust gases is potentially very  corrosive, a corrosion-preventive mixture must be sprayed  into each exhaust port, including the exhaust valve. After  the exhaust ports have been thoroughly coated, a moisture- proof and oil-proof gasket backed by a metal or wooden plate  should be secured over the exhaust ports using the exhaust  stack mounting studs and nuts. These covers form a seal to  prevent moisture from entering the interior of the engine  through the exhaust ports. Engines stored in metal containers usually have special ventilatory covers. Another point at  which the engine must be sealed is the intake manifold. If  Engine Preservation and Return to Service 8-20