In the C336 Service Manual it states that the auxiliary fuel tanks capacity is 19 gallons of which 18 gallons are usable. See the first attachment.
The main tank system (two interconnected tanks) have a capacity of 46.4 gallons each. If the C336 has 128 usable fuel then this would allow the mains to have 46 gallons usable each. Leaving 0.8 gallons unusable. See second attachment
Third attachment is the C336 fuel schematic.
The main tanks have an aft connection and a forward connection on the inboard main tank. The outboard main tank is interconnected to the inboard main by an upper and lower front connector and a lower aft connector. These connections are depicted on the schematic attached. Here is a photo of the tank
http://www.337skymaster.com/messages...ead.php?t=2309
As pointed out on Ernie's site, when on extended flights the auxiliary fuel tanks should be use as soon as possible (60 minutes from departure) after mains have been used at least 1 hour. This is because the auxiliary tanks can not be used for landing. The electric fuel pumps will not provide fuel from the aux's if a engine driven pump fails and the aux's cannot crossfeed to opposite sides for front / rear engines. Therefore, I always use my aux tanks as soon as possible on long trips. Keep all the fuel you can in the mains for emergency issues that may arise.
Hybrid Mode
