Gravity feeding auxiliary tanks

[Jeff@QuadShop]

Ok, my 89 Mazda B2600i stock tank is only 11 gallons which really sucks for the expedition travel that I like to do. I know I can carry gas cans but I really don't like this idea.
I'm going to have a 12 gallon in bed tank built which will get me just over 400 miles between fill ups. My question is, can I just run a hose from the bottom of the auxiliary tank and T it into the stock rubber filler neck on the truck? Or will the trucks stock filler cap leak once the main tank is full? Would just doing away with the stock filler cap and running the filler hose directly to the bottom of the auxiliary tank work better?

 

[cocco78]

You could just put a petcock type valve on your aux tank, when you main tank gets low just open the valve to fill your main tank back up...

 

[Jeff@QuadShop]

You could just put a petcock type valve on your aux tank, when you main tank gets low just open the valve to fill your main tank back up...

I'd rather not mess with that if I don't have too.

 

[rickc]

Hi Jeff:

I think you misunderstood cocco78's response - it's a good one. As long as the aux is higher than the main then you can use it like a big jerry can; just direct it to the main tank filler via a direct hard pipe and small valve or use a flexible hose. Will the new tank have internal baffles? How is it vented?

 

[Payback]

I'm pretty sure the stock fuel cap would prevent leakage. Yours should be air-tight, which would suggest it's liquid-tight. That being said, I would probably just bypass the stock filler and just tie straight into the aux tank. The original fuel cap wouldn't serve any purpose as you wouldn't be able to open it as long as there was fuel in the aux tank. You're going to have to figure out how to vent the lower tank into the aux tank to prevent it from have a huge bubble of air/fumes stuck inside. I could see that getting sucked into the fuel line and flaming out your engine.

 

[corax]

Couple issues with that right off the top of my head, the first being that having a tank in the bed puts it at or above the level of the charcoal canister which may lead to fuel backing up into it. If that happens expect a stalling condition or poor drivability as the intake sucks raw fuel in

The second being that you won't get much gravity feed without a vent line from the main tank to the aux tank (or vent the aux tank to atmosphere which is not recommended) - put a hose in the end of a 2L bottle and turn it upside down, you'll notice water runs out for a few seconds and then stops from vacuum build up.

your simplest/best bet would be a petcock (electric or manual) to drain the gas into you main tank when it gets empty + "T" into the evap vent line on the main tank for the aux tank vent. When I installed my aux tank I did it with electric pump transfer

 

[ntsqd]

At one time there was a Fed regulation restricting gravity feed fuel systems to diesel only vehicles. Do not know if that is still the case or not. It came about during the early 70's fuel crunch when people burned to death because of gravity feed systems leaking gasoline due to over-filling the original tank.
Tread carefully here. I'd advise a larger main tank.

 

[Jeff@QuadShop]

My plan is to take out the stock filler neck and weld it to the top of the aux tank. This neck has an external vent nipple comming out of the side meaning I can run the stock tank vent to this nipple just like stock.

Doesn't the stock gas cap let air in for venting but won't let air/gas out? I can always relocate the charcoal canister higher up in the engine bay if there is a flooding issue.

I really don't want to mess with a pump or turning of a valve. I just want to fill up from the aux tank and not touch it again untill it's time to gas up.

I don't see where baffels will be needed for just 12 gallons.

There are no larger main tanks available in the US for my truck.

 

[sapper]

What I have used for years, at least 10 so far on the same one.

http://www.supersyphon.com/SuperSyphon.html

Very easy. No mods required just have to stop, shake and fill your tank.


I have 4, 5 Gal jerry cans in the bed and I don't even have to unmount them to fill my tank, I just extended the clear hose.

Just make sure you have enough space in the tank for the fuel.


The reason it is illegal for gravity feed tanks is because if there is a leak your entire tank will leak onto the ground and there is nothing to stop it in most cases. Also diesel will actually eat the road unless concrete and destroy it.

 

[Albin]

I had an Auxiliary Fuel Systems 15 gallon gravity feed tank on my old '85 Nissan and now have a 26 gallon gravity feed aux fuel tank for my '85 4runner, giving me a total of about 45 gallons with the OEM and one five gallon jerry can.

A bunch of good info in this thread, especially given that you plan to gravity feed a gas powered vehicle.

Some comments:

- I'd use a simple ball valve, at a minimum, to control feed into the main tank. If you need faster refueling, I'd use a small fuel pump.

- "Refuel" while stopped. Given the enviro equipment on most gas powered vehicles, such as the afore-mentioned charcoal canister, I wouldn't risk refueling while driving. My .02.

- You will need to tie the vent lines of the two fuel tanks together or vent the aux fuel tank to open air via a small fuel filter, and locate it so that it can't suck in water or allow water to fall into it. On my 4runner, I connected the aux and OEM vent lines together. On my '06 PSD, I vented the aux fuel tank to open air.

Gravity feed of gas powered vehicles isn't illegal per USDOT per se. The applicable USDOT regulation is 49CFR393.67(c) (5), Liquid Fuel Tanks, Fuel Withdrawal fittings: "(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." This is the regulation that typically precludes gravity feed in gas powered vehicles.

Having said that, there is at least one manufacturer of gravity feed fuel tanks for gas powered vehicles (NW Metal Products). I used their 4runner OEM fuel tank fitting to install gravity feed in my 4runner. How they got around the above DOT regulation is unknown to me. I plan to remain ignorant on this subject for my application....

One other thing I would add between the aux and OEM fuel tanks is a fuel filter. I have a small 3/8" Fram fuel filter on my 4runner and a large 12 micron water fuel filter separator on my PSD. Never miss a chance to filter your fuel.

Good luck.

Al

 

[Alltwistedup]

On my last truck a 1 ton Dodge dually gas v10 that got 13 mpg down hill in Colorado with the wind pushing it and 7 mpg towing my 5th wheel. I opted to put in an aux tank in the bed so that I could go past at least 2 gas stations in a row. The setup worked like this: removed stock gas tank and put two bulkhead fittings in the top then reinstall. One fitting had a piece of hose 4” long in the tank this was the vent fitting. The other fitting nothing inside this was the fill fitting. On the aux tank at the center bottom front the was a fitting straight to a valve and then hard pipe with a 6” rubber hose to the fill fitting. On the 3” filler neck of the tank their was a fitting I welded in that went straight to a valve and then hard pipe with a 6” rubber hose to the vent fitting.

Worked like this.
With the main tank full and the aux tank full with valves off it was 35 gallons.
With the main tank full and the aux tank full and valves on it was 35 gallons until the main tank level dropped below the 4” vent hose then the aux tank could vent until it supplied fuel to cover up the vent hose. So as I drove the main tank constantly re fueled itself thanks to gravity and vent control. My fuel gauge would just to go ¾ full and stay their for 700 miles. When the fuel gauge stated dropping again I knew the aux tank was empty and it was time to start looking fill up 100 gallons.

I always turned the valves off when I was just running around town or had a full main tank due to small aux tank air leak if the main tank got to much fuel it leaked out the pump/gauge sending unit all over the ground. When it was all said and done I could fill both tanks in Colorado Springs, CO and drive past Chicago without stopping for fuel on my way home to Detroit. Thanks to Gas Buddy.com the whole thing paid for itself on big trip as I found cheap prices and just filled up their and save $10-15 each time. When gas prices sky rocked from the back to back hurricanes in 2005 I paid the same price even though I had an 80 mile daily commute, I only filled up once a month LOL.

 

[thebrassnuckles]

I had an Auxiliary Fuel Systems 15 gallon gravity feed tank on my old '85 Nissan and now have a 26 gallon gravity feed aux fuel tank for my '85 4runner, giving me a total of about 45 gallons with the OEM and one five gallon jerry can.


Al

Do you have a write up of your AUX tank install?
I have an 85 runner and am looking to get more fuel capacity.

 

[Albin]

No, sorry, not on the Toyota.

Basically, I took a 26 gallon Blazer NOS diesel fuel tank I got from Coleman's Surplus (PA), made my own mounts and installed it where the spare tire originally went. I had to cut out the spare tire cross brace.

Since the tank was new and never held any fuel, I had no trouble drilling a hole on the lower right front end of the tank for a 3/8" NPT nipple, then welding it in. I used a McMaster-Carr 3/8" ball valve to control flow from the aux tank to the OEM tank. I used the North West Metal Products Toyota replacement drain plug fitting to get the aux fuel to the OEM tank. Used about 12" of fuel fill hose from Napa and a piece of exhaust tubing plus a spare 4runner fuel cap to get the fuel to the aux tank. The fill cap comes out above the frame at the back end of the passenger rear tire.

Essentially, I bought the tank sight unseen, CS had a pic and dimensions, and made it work. Unfortunately, CS no longer shows this tank on their site. Lots of people use F-150 or Ford van 26 gallon tanks for use as an aux fuel tank for the 4runners, installation should be about the same except most of the installations I've read about, people use the Ford OEM fuel pump for fuel transfer instead of gravity feed.

Al

 

[Wheelingnoob]

No, sorry, not on the Toyota.

Basically, I took a 26 gallon Blazer NOS diesel fuel tank I got from Coleman's Surplus (PS), made my own mounts and installed it where the spare tire originally went. I had to cut out the spare tire cross brace.

Since the tank was new and never held any fuel, I had no trouble drilling a hole on the lower right front end of the tank for a 3/8" NPT nipple, then welding it in. I used a McMaster-Carr 3/8" ball valve to control flow from the aux tank to the OEM tank. I used the North West Metal Products Toyota replacement drain plug fitting to get the aux fuel to the OEM tank. Used about 12" of fuel fill hose from Napa and a piece of exhaust tubing plus a spare 4runner fuel cap to get the fuel to the aux tank. The fill cap comes out above the frame at the back end of the passenger rear tire.

Essentially, I bought the tank sight unseen, CS had a pic and dimensions, and made it work. Unfortunately, CS no longer shows this tank on their site. Lots of people use F-150 or Ford van 26 gallon tanks for use as an aux fuel tank for the 4runners, installation should be about the same except most of the installations I've read about, people use the Ford OEM fuel pump for fuel transfer instead of gravity feed.

Al

The Ford F-150 tank is on my list of mods too, I want to have that extra range when I need it with out Jerry cans all over my roof or rear bumper.

 

[Albin]

Yep, it's nice being able to drive +500 miles and pass this without a care in the world: