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Old 05-29-2008, 09:08 AM   #1
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Secondary fuel tank

When I test fuel additives, I hate having to burn off 20 gallons of fuel before I can move on the another product to test, and There is always enough fuel left that I wonder if the results will be totally accurate. And, I do not trust gas station pumps to be accurate enough for the kind of testing I want to do. I know they are calibrated and yadda yadda yadda, but anything the government says is ok is suspect in my book!
I have been playing with the idea of a installing a 5 or 6 gallon auxiliary fuel tank to use for fuel additive testing, so I only have to burn off 5 0r 6 gallons of gas instead of 20 before I can test the next additive.
I would build a steel enclosure in the back of my van, with a hatch on top to get the removable tank in and out, so I could fill the tank outside on the ground. The hatch would be gasketed and sealed to keep out any gas fumes from the passenger area.
The enclosure would have holes in the floor for good ventilation.
I was thinking of using a marine gas tank, portable kind, modified for the appropriate vapor and venting fittings, which would all go into the existing vapor recovery system.
I would use a regular low pressure fuel pump to draw fuel out of the tank and feed it to a high pressure pump mounted under the van bloted to the underbody. Very much like the late 80's early 90's F series Ford trucks were setup.
I would use an appropriate dual tank switch valve to switch tanks from the dash.
There would be a way to pump the fuel in the secondary tank to the primary tank so I could always start out whet fresh fuel in the secondary tank for each test.

Any thoughts?

Thanks
WorkingOnWise
aka Keith
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Old 05-29-2008, 10:32 AM   #2
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It sounds like you'll do too much reinventing the wheel. Consider using more components from existing dual tank systems found on pickup trucks, and for the tank itself, use an automotive racing fuel tank, especially if you're going to have it in the passenger/cargo area.

Don't modern fuel injection systems include a return line that sends some gas back to the tank? Would you have to plumb that too, in order to avoid contaminating your main tank?

Is there space under the hood for the tank?

You may want to make it easy to remove with quick-disconnect fittings. If you do that, it becomes very easy to VERY accurately measure your fuel usage by weighing the tank before and after.

I'm interested in the system you mentioned on the 80s F-series, as I have a carbureted vehicle that I'd like to convert to TBI but I'm intimidated by having to replace the tank and all the lines in order to get the high pressure system I need. Can you tell me more about it and how I might apply it to my situation?
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Old 05-29-2008, 11:20 AM   #3
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Reinventing the wheel

The marine fuel tank I mentioned is designed to be removable. It's one you would find on small boats with smaller outboards.
The reason I dont do a more conventional underbody mounted secondary tank is because I dont want to go thru all the sheet metal work of installing a second fuel filler door and neck. I am doing this on a 1995 Mercury Villager minivan, so there isne really much roog to do it and have it look clean. I promised my wife that whatever I did to the van it would not be to outlandish or sloppy. She shot down the rear boat tail before I finished telling her what I was! Go Figure!

I hadn't thought of a race car fuel tank (fuel cell). That would be much safer that the marine fuel tank, and I could still make it easily removable.

Yeah, removing it is exactly what I want to do, to get the most accurate consumption numbers I can. And since the only good place to put it is in the passenger area (in a box that will not let any fumes or liquids out, except to the outside, under the van)

As for the dual tank system, Fords have had dual tanks for a long long time. The system I am most familure with is the 88-91 system, which I dont like. There is a low pressure pump in each tank that feeds to a switch valve. after the switch valve is the high pressure pump to feed the EFI. The switch on the dash turns the right pumps off and on based on the switch position you pick. The switch valve switches based on fuel pressure. Rear pump turns on, causing the valve to isolate the front tank, and letting the rear tanks fuel flow to the high pressure pump.
Pretty simple system, and inexpensive.
Trouble is, when that valve fails, it can allow some fuel to bleed into the tank that is supposd to be off, so you actually can fill one tank from the other, and there is nothing to stop it from overfilling and backing up into the vapor recovery system and leaking all over. Not a good thing! It happened on my old truck, but I had one tank half full, the other almost empty. When I "ran out" of gas, I thought there was no way that was possible. I switched to the other tank, that I had emptied the day before, and magically it had over a 1/4 tank!
Because of that, I'll be using an electric switch valve from JC Whitney. I wont need to worry about fuel level, so the sender wont be needed. Another reason the fuel cell looks good. No sender to complicate things.

EDIT - fuel cell here is a fuel tank with closed cell foam in it, preventing much, if any, fuel leakage in the event of a puncture. Not the catalytic thingys that are to save the world when someone figures out how to build them for a dime a dozen! (sarcasm from a guy who is getting tired of waiting for all this technology that will probly never make it to my driveway!) On theholycows advice to keep it clear. Thanks
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Old 05-29-2008, 11:51 AM   #4
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If you don't like Ford's 88-91 dual tank system, you might want to look at competing systems from GM and Chrysler. They all have had them for decades and probably continue to have them on some new trucks. I had a 1997 F350 dumptruck with Ford's dual tank system which may have been improved over the 88-91 setup. It never gave me any trouble, though we did have a fuel pump in one tank go bad once.

I hesitate to call racing fuel tanks "fuel cell" here because I don't want to confuse anyone who might think I'm talking about catalytically generating electricity from hydrogen. I am familiar with the marine tanks and they're a bit lame for this application.
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