Four-stroke engine oil resevoir  for checking oil with dip stick Figure 5-60. Four-stroke engine showing the oil reservoir where  the dip stick is located to check the oil. Figure 5-58. Checking the flight deck instruments for readability  and security. Turning on the main electrical power to verify proper  instrument readings. Figure 5-59. Translucent fuel containers with premixed oil (right)  and auto gas only (left). on a limited basis but the lead in this is not good for the engine  and additional precautions/procedures should be researched for  the particular make/model of engine for primary use.  of oil during normal operation. If consumption grows or  suddenly changes, qualified maintenance personnel should  investigate. Always use a higher grade/octane of fuel rather than a lower  grade, or detonation will severely damage the engine in a very  short period of time. Check the aircraft operation manual and  the engine manual for the type of fuel to use.  When attempting to fuel for maximum capacity, remember  that many fuel tanks are very sensitive to attitude. Fill the  aircraft on a level surface and check to ensure the amount  of fuel in the tanks is adequate for the planned flight plus 30  minutes of reserve. Check the level in the fuel tank plus the  panel-mounted gauge, if so equipped. If the Rotax 912 oil level is low when the oil is checked,  rotate the propeller in the correct direction (counterclockwise,  facing it) to pump any oil from the engine back into the oil  tank for a proper measurement and recheck oil level before  adding oil.  [Figure 5-60] To transport gasoline, clear gas cans are preferable because  the fuel is visible through the container and allows a pilot to  look at the container for fuel level.  [Figure 5-59] An important step in any preflight is to check for water and  other sediment contamination. Avgas is more probable to  have water in the fuel tanks because auto gas typically has  alcohol in it to boost the octane. Alcohol absorbs water,  running it harmlessly through the system. When using 100LL Avgas, water tends to accumulate in  fuel tanks from condensation, particularly in partially fi lled  tanks. Because water is heavier than fuel, it tends to collect  in the low points of the fuel system. If Avgas is used, drain  any water from the low point in the system.  A four-stroke engine’s oil level should be checked during  each preflight and rechecked with each refueling. Four- stroke engines can be expected to consume a small amount  Check the reservoir level of two-stroke engines with oil  injection at each gas fill-up. It is also very important to ensure  the oil reservoir has clear air vent holes to allow continuous  flow of oil to lubricate the engine. Always use the same type  of oil because different types of oil harden and stop the oil  injection process, resulting in a seized engine. Additionally,   Oil 5-21