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Cessna 172 Supplement

Terms in this set (89)

Late model: The fuel system consists of 2 integral tanks in the wings with a total fuel capacity of 56 gallons, of which 53 is usable. Three gallons remain unusable because fuel is drawn from slightly above the bottom of the tanks, to avoid drawing contaminants into the engine. Usable fuel quantity is placarded on the fuel selector. Typically there are 13 fuel sumps: 5 under each wing and 3 under the engine cowling. There are 3 fuel vents: 1 under the left wing and 1 in each fuel cap. Fuel is gravity-fed from the wing tanks to a three-position fuel selector valve labeled BOTH, RIGHT, and LEFT, and then to a reservoir tank. From the reservoir tank the fuel flows to an electrically-driven auxiliary fuel pump, past the fuel shutoff valve, through the strainer and to an engine-driven fuel pump. Fuel is then delivered to the fuel/air control unit where it is metered and passed to a manifold where it is distributed to each cylinder. The auxiliary fuel pump is used for engine priming during cold engine starts. The auxiliary fuel pump is OFF for normal takeoff and landing operations.

Fuel-injected engines do not have carburetor heat like early-model, carbureted engines. Alternate air is provided with a spring-loaded alternate air door in the air box. If the air induction filter should become blocked, suction created by the engine will open the door and draw unfiltered air from inside the lower cowl area. An open alternate air door will result in approximately 10% power loss at full throttle.

Early model:
The fuel system has a total usable fuel capacity of as little as 38 gallons (usable fuel is placarded on the fuel selector). Typically there are 3 fuel sumps (1 under each wing and 1 under the engine cowling). There is no electrically-driven auxiliary fuel pump. There is no separate fuel shutoff valve. In lieu of a separate fuel shutoff valve, the fuel selector valve has an OFF position. Fuel is delivered to a carburetor.