Gravity-feed: Is it Legal?
There two kinds of extra fuel tanks - auxiliary and refuel. You don't have an auxiliary tank - you have a refuel tank. Normally, refuel tanks are used to haul fuel to other vehicles, such as tractors or off-road equipment. But it can also be used to haul extra fuel for your pickup.
It sounds like your refuel tank is hooked up to be legal per DOT rules. It works, so love it.
But if you want to convert it to an auxiliary tank, it's not simple. You cannot simply plumb in a gravity feed into the main tank. That's a DOT no no.
The best way to hook up an auxliary tank and be legal is to buy the tank and other stuff from Transfer Flow's Trax-II
. Then you have an integrated system and your fuel gauge will work right. But I doubt TransferFlow will sell you just the stuff you need to convert yours into an auxiliary tank unless you also buy their tank. But it won't hurt to ask them.
Look closely at your tank. If it has a plug or two at the bottom of the tank, then it can probably be converted to an auxiliary tank without having to clean the tank and add a welded-in threaded bung.
Yep. That's the cheap way to add more fuel capacity. Auxiliary tanks with all the valves and plumbing and wiring cost a lot more.
From TransferFlow, an 82 gallon refuel tank costs $654. But a 75-gallon auxiliary tank with the wonderful Trax II system costs about $1,100.
Where there's a will, there's a way. But it won't be easy and it probably won't be cheap. I'd start with TransferFlow and see if they will sell you the Trax II and other parts you need without having to buy a new tank. If they won't, then you'll have to do some shopping.
There is probably more confusion on this subject than any other in the discussion of aux fuel
tanks for pickup trucks. What follows here is the relevant regulation from the Department of
Transportation (DOT) Code of Federal Regulations (CFR). However, I am not a lawyer nor is
any of this discussion to be construed as legal advice; it’s simply provided for your use as a
basis for further investigation for your own information and use.
The relevant portions of the DOT CFR codes that apply to gravity feeding of fuel tanks are
49CFR393.65 Fuel Systems and 49CFR393.67 Liquid Fuel Tanks. The relevant portions of
these sections are as shown below. For a complete copy of the entire texts, see the link for
the DOT in the Appendix and then follow the link to the 393 section of 49CFR.
49CFR393.65, Fuel Systems: “(d) Gravity or siphon feed prohibited. A fuel system must not
supply fuel by gravity or siphon feed directly to the carburetor or injector.” [Ed. Note:
misspelled word corrected.]
Note that 393.65(d) title makes a declarative and complete sentence with an adjective, noun
and verb i.e. “Gravity …. feed prohibited”. Quoted out of context, it is easy to see how people
say that “DOT prohibits gravity feed”. However, this sentence is not a regulation, it’s a
paragraph title and it is completely negated by the actual regulation that follows it i.e. “…
must not supply fuel by gravity … feed directly to the carburetor or injector.” Since I am
supplying fuel via gravity feed to the OEM fuel fill line and not directly to any carburetor or
injector, I see no violation of 393.65.
49CFR393.67, Liquid Fuel Tank (partial): “c) Construction of Fuel Tanks, (5) Fuel withdrawal
fittings. Except for diesel fuel tanks, the fittings through which fuel is withdrawn from a fuel
tank must be located above the normal level of fuel in the tank when the tank is full.”
Since I am withdrawing diesel fuel and only diesel fuel from the bottom drain fitting of my aux
fuel tank, I see no violation of 393.67 with my aux fuel tank functional design.
There are other regulations that apply to fuel tanks and systems at the Federal level, mainly
Federal Motor Vehicle Safety Standards and environmental regulations. Vehicle safety
standards for gravity feed mainly follow DOT as far as I’ve seen; if so, I see no violation there.
Environmental regulations have to do primarily with leaking fuel.
There are a number of regulations that you need to be aware in installing your aux fuel tank;
these are called out in 49CFR393.65, Fuel Systems. Examples include not having any fuel
lines near flame or heat sources (i.e. the exhaust system); not having fuel lines outside the
body of the vehicle or in the interior/passenger area of the vehicle. Anyone installing an aux
fuel tank in their vehicle should review these regulations in their entirety to ensure their
installation meets all DOT and Federal Safety requirements.
Basically, if you install the aux fuel tank using the same or similar workmanship and parts
standards as the OEM design, you should have no problems with either safety standards or
with leaking fuel. Note that any leaking fuel is a violation regardless of whether or not your
fuel system is completely OEM or has been modified with the addition of an aux fuel tank.
From here: http://www.rocketcityrockcrawlers.co...2007-06-18.pdf
All DOT rules and regulations: The Code of Federal Regulations