How to (properly) do an aux fuel tank? - Diesel Forum - TheDieselStop.com
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1999-2007 Upgrades and Aftermarket - General Upgrading or adding OEM or aftermarket equipment to your 1999-2007 Super Duty. Please confine discussion of topics in this forum to those items that are not engine-specific.

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Old 03-18-2008, 12:07 AM   #1 (permalink)
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How to (properly) do an aux fuel tank?

I have a new to me 2000 F350.. upgraded from my 96 F350.. what a deal

This has an external fuel tank in the bed...

The guy has 2 complete fuel systems... 2 pumps, 2 filters, etc.. and a switch in the cab to change tanks.

I have 2 issues / questions about this.

#1: is that the right way to do it? I thought aux tanks were gravity fed into the stock tank.

#2: There is no fuel guage on this thing - the guy was using a broom stick.

What are my solutions? Is there a way to make a working fuel guage on the external tank?

I realize that I'm leaving out some details... if you have specific questions... I'll see what I can do... I still haven't completely gone through the truck to figure out what and were everything is....


Thanks for the help...
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Old 03-18-2008, 06:28 AM   #2 (permalink)
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I would think the in-bed tank fills the OEM tank, I couldn't see him using it to feed the motor. The broom stick is a tried and true method of checking the fuel level.

Do you know the in-bed tank size?
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Old 03-18-2008, 06:40 AM   #3 (permalink)
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I was told that it's 100 gallons.

Is there a writeup on how to do something like that?

I may have to find a way to un-do what this guy has done - ugh!
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Old 03-18-2008, 10:24 AM   #4 (permalink)
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Quote:
Originally Posted by ChrisJohnson00TA View Post
#1: is that the right way to do it? I thought aux tanks were gravity fed into the stock tank.
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.

Quote:
#2: There is no fuel guage on this thing - the guy was using a broom stick.
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.

Quote:
What are my solutions? Is there a way to make a working fuel guage on the external tank?
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.
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Old 03-18-2008, 11:39 AM   #5 (permalink)
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Slightly confused because he said he has a switch in the cab to switch tanks.
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Old 03-18-2008, 12:03 PM   #6 (permalink)
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Quote:
Originally Posted by SmokeyWren View Post
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.

Gravity-feed: Is it Legal?

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
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Old 03-18-2008, 02:31 PM   #7 (permalink)
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Slightly confused because he said he has a switch in the cab to switch tanks.
The switch in the cab changes a valve that selects which fuel line (and fuel pump), the line and pump from the stock tank or the line and pump from from the refuel tank. The refuel tank is not gravity feed - it has a pump that pumps the fuel up out of the tank and into the fuel line to the engine.

I had something similar 50 years ago, except it was gasoline in the stock tank and and propane in the extra tank in the bed, instead of diesel and diesel. My fuel gauge only worked on the stock tank. So usually we'd drive on propane until it ran out, then switch to gasoline and use the gas gauge until we could fill up again. If you quickly changed the valve after the first miss of the engine because you "ran out of gas", you wouldn't lose much speed. "Gas" mileage fell about 20 percent on propane, but it cost only $.07 per gallon for "tractor gas" propane back then, so we didn't worry too much about gas mileage.

After I left for college, and before I-20 was built, Li'l Bro filled up both tanks and drove 320 miles to see his girl in El Paso, then drove the 320 miles back and got home before sunup so Daddy wouldn't know how dumb he was. Of course, the next day sitting on the tractor all day made for a long, long day.
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Old 03-18-2008, 02:35 PM   #8 (permalink)
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Thanks for the input everyone.

Yes, I do have a switch in the cab to change tanks.... I guess similarly to how my 96 worked.

It appears to me that what I *thought* would be the right way, is the wrong way.

I'm fine with having to switch tanks... just wish that there was an easy way to tell how much fuel I had in the aux tank.

Here are some pics with some fuel tank pics at the end.

2000 F350
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Old 03-19-2008, 12:17 AM   #9 (permalink)
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You have a few options:
1. Put a sender in the tank - either into that fill port on the drivers side or cut a hole in the tank like the semis use and wire it to an auxiliary gauge in the truck. That would give you the info in the cab.
2. Put a gauge in the tank. You would have to stop to read the level but it will work.
3. Some sort of clear tube along the side of the tank with a fitting top and bottom that would have fuel in it at the same level as in the tank.
4. I am no electrical guy but I am sure that a sender could be installed in the tank. When you would switch tanks it would also switch which sender was feeding inputs to the stock gauge. Isnt this how the stock setups worked with dual tanks?
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Old 03-19-2008, 08:00 PM   #10 (permalink)
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i have a 115 gal aux tank. the switch in the cab switches between tanks. Mine has a sending unit in it so the stock gauge tells me how much is in the tank. It does not fill the stock tank. One of my drivers dodge is setup to fill his stock tank. he has a fuel pump that turns on by switch and fills his main tank.
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Old 03-21-2008, 07:38 PM   #11 (permalink)
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You could install one of these.....

Auto Meter 3262 - Auto Meter Fuel Level Sender - JEGS

and hook it up to one of these in the cab......

Auto Meter 4316 - Auto Meter Ultra-Lite Gauges - JEGS

so you won't have to use a broom handle.
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Old 03-21-2008, 10:17 PM   #12 (permalink)
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might want to add an extra filter between the aux pickup and your final filter.
otherwise your be changing your fuel bowl filter more often..
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Old 03-21-2008, 11:19 PM   #13 (permalink)
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Originally Posted by southmike View Post
might want to add an extra filter between the aux pickup and your final filter.
otherwise your be changing your fuel bowl filter more often..
Already have 2 'pre' filters before the fuel bowl.

Thanks (everyone) for the input... I need to look at my tank and see if I can easily mount one of those senders.
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Old 05-10-2008, 03:52 PM   #14 (permalink)
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I skipped most of the posts, so excuse me if this was mentioned. Two fuel tanks with two pumps and a solenoid switch to choose which one sounds very much like he ran oil in it. Maybe you don't even have a diesel, I don't know. If you do and you don't know he didn't, maybe check to see if any of the lines on the aux. tank look they were heated anywhere. If not, you sound pretty close to being able to run vegetable oil in your truck if you want.
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Old 06-10-2008, 07:02 AM   #15 (permalink)
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Quote:
Originally Posted by SmokeyWren View Post
There two kinds of extra fuel tanks -

[snip]

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.

[snip]
Not true, it's specifically allowed by the DOT/FMCSA.
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