>In a message dated 7/5/2000 10:23:41 AM Central Daylight Time,
>
> first, then switch to my Main as a reserve. That's my way. >>
>
>I may not understand everything I know about this, but it would appear to me
>that although the Onan physically draws from the rear tank, it is in effect
>taking equal amounts from each tank since the tanks are connected and liquids
>seek their own level. The system is designed so as to prevent the Onan from
>being able to drain the fuel supply, and (theoretically) precluding the
>possibility of leaving you stranded in the boondocks. So, if you start with
>both tanks full and run the Onan 48 hours burning .9 gals/hr., you'll have
>approximately 7 gals of gas left when the Onan starves out. Won't this 7 gals
>be evenly distributed between the 2 tanks, and if so, what difference does it
>make which tank you start toward town on?
>
>Lanier Foote
Hi Lanier. You are correct up to a point. If the two fuel tanks
were connected at the bottom of the tanks you would be 100% correct.
However, The two fuel tanks are connected at the side by the inlet
filler pipes. This connection is about 1/3 to 1/2 of the way up from
the bottom of the tanks. If the GMC is level, the fuel is drawn
equally out of both tanks because of this connection (fuel will flow
from one tank to the other through this connection). Once the fuel
level is below this connection the fuel that is drawn from one tank
will empty that tank while about 7 to 10 gallons of fuel is still
left in the other tank. In the case of the Onan, the fuel pickup
tube in the main tank (the rear one) is somewhat above the bottom of
the tank. If you started with two full tanks and ran the Onan until
it stopped from lack of fuel, you would first draw down both fuel
tanks until you reached the point where the fuel falls below the
level of the pipe that connects the two tanks. You would then draw
down the main tank until the Onan pickup starts to suck air. At that
point you would have approx. 1/3 tank of gas in the front (aux) fuel
tank and you would have a few gallons of fuel left in the main tank.
I have found that the point where the Onan stops picking up fuel from
the main tank leaves about 4 or 5 gallons in the main tank.
The reason the Onan pickup tube was left short of the tank bottom was
to prevent someone from draining their Aux. tank while driving and
then camping in the boonies and using their Onan and possibly using
all of their fuel from the main tank and not being able to get the
GMC back to civilization. You cannot drain all the fuel from the
main tank with the Onan and the amount of fuel left would hopefully
get your GMC to a service station.
If you camp with an empty main tank, your Onan will not operate even
though you may have 7 to 10 gallons of fuel in your Aux. tank.
Emery Stora
77 Kingsley
Santa Fe, NM
