Thinking Of Plumbing My Two Tanks Together

[Poorman]

So I've been crawling all over my truck trying to fix any air intrusion leaks on my "86" 6.9 f350 dually 4 door. Today while laying under the truck looking at the Fuel Tank Selector Valve (FTSV) I had a thought. Why couldn't I stick a line into the bottom of the rear tank and run it level up to the front tank which would put it about mid height or 7" up from the bottom of that tank. Then I could get rid of the FTSV and the two lines running back to the rear tank. I just hate the electronic valve, every time I'm in the middle of nowhere and I go to switch tanks I have a panic attack. I know someday it's not going to work, or it will run the return to the wrong tank. The fuel gauge likes to drop to empty at times and that gets your heart racing even though it's almost full, which is probably the sending unit. I'm all about simplicity, that's why I have an IDI. Why wouldn't it work?? Any ideas on how to get a fitting plumbed into the tanks, braze? rubber seal?

 

[Kdo58]

I just put a large rear tank in mine and removed the front tank.

 

[Poorman]

What did you do with the spare tire? or did you put it in the bed?

 

[Kdo58]

I have a canopy

 

[Old Goat]

What did you do with the spare tire? or did you put it in the bed?

I installed my spare in the bed. Came across one the Ford options for a in bed
Tire Mount. Mounts to the left front. Post one in the following thread shows the
hardware.

Factory In Bed Spare Tire Carrier - Ford Truck Enthusiasts Forums

1987 - 1996 F150 & Larger F-Series Trucks - Factory In Bed Spare Tire Carrier - Hey Folks! I thought my latest project may be of interest to the group so I thought I would post a quick write up and some pictures. I went with the in bed setup because the under body system is terrible to actually...

www.ford-trucks.com

You would be better off replacing the rear 19 gallon tank with a Spectra F-26-E
38 gallon tank. Then maybe use the front tank for a transfer tank to pump to the rear.

Found this drawing of the parts.
I have # 1405 & 1407 and the nuts and bolts that came with it.
Got it off a friends truck.

You must be registered for see images attach

Goat

 

[Poorman]

I'm happy with my fuel capacity, so an aftermarket larger tank that would displace my spare tire isn't something I'm interested in. I always have a 12 foot camper on and a small trailer packed with motorcycle, generators, fuel cans, spare trailer tire, propane tanks, bicycles, ect., no room for truck spare, not even close.
So I'm really seriously thinking of linking the two tanks, I need to pull the tanks and probably replace the sending units anyway so that would be the time to poke a hole in them. They're only about a foot apart so a short piece of 5/16 fuel line and a couple of fittings, maybe fabricate a small metal guard so the fitting doesn't get hit when putting the spare up in it's rack, it looks easy.
If I do this I'd like to get rid of the hard plastic line that runs from the metal line back to the FTSV, question, would regular rubber fuel line be the way to go, or is there something better??

 

[Kdo58]

The problem I've read is the return lines, it will over fill one of the tanks.

 

[asmith]

I would think if you plumbed your tanks together you would want to go as low as possible on both of them so that the level is as close to equal in both of them. Basically then you would have one large tank and wouldn't need to switch back and forth between them. You could even get rid of one of the senders and return. Just leave the switch on the tank that has a functioning sender. Filling may be a little slower depending on how big of a hose you put between them. CDD has a sump fitting for the rear tank. maybe something like that.

 

[Poorman]

ASMITH, you're getting it pretty close, I plan on installing a very small line between the two (5/16), when filling up it wouldn't be transferring much fuel thru the line, I would just fill both tanks using their own spouts, just like now, a small amount would gravity feed to the other tank via the new small line but that would stop as soon as I put the fill spout in the other tank. I would go as low as possible with the new line on the rear high tank but mid height on the front tank, that way if ever there was a problem with the new line it wouldn't leak out the whole tank and mid height would allow the rear tank to drain completely into the front tank via gravity. Yes it would allow the removal of the sending unit and return line to the rear tank. It will cause the fuel gauge to work a little weird, it will go down real slow until the rear tank is empty and then speed up as it finishes off the front tank, should be easy to get used to.

 

[Cubey]

$100 for a lifetime warranty valve at AutoZone is the best option really. Then things will work properly and you never have to buy one again if it breaks or leaks. buy the kit with the switch and pigtail. toss the switch to the side and and use the pigtail if needed for older style valves.

 

[IDIBRONCO]

Why wouldn't it work??

The problem I've read is the return lines, it will over fill one of the tanks.

I think it would work IF you used a big enough line. Like Kdo said, it would overflow one of the tanks. Look at semis. At least some of them do this, but they use a MUCH larger line than 5/16". It's probably 1" or bigger.

 

[Poorman]

IDIBRONCO, I'm not following you're reasoning, and I'd like to, I don't want to make a blunder here. If I'm only pulling fuel from the front tank and only returning fuel to the front tank, how could it overflow either? the rear tank will always seek the same level as the front tank rather it's a 1/8" line between them or a 2" line, it would in reality just be one tank with a bulkhead in the middle. Remember the tops of the tanks are level with each other, I could see an overflow problem if I pulled from the front and returned to the rear and had an 1/8 " line between the two tanks, but that's not the intention. THANKS to all for helping me think this thru

 

[ISPKI]

The fuel feed lines are 3/8" and the return is 5/16". I think the issue is that the fuel is returning to your tank under pressure thru the 5/16" line but it is feeding by gravity from one tank to the other. The lift pump is fed by and feeds a 3/8" line until it hits the fuel filter and it feeds at what 5 or 6 psi? Some losses are experienced throughout the system, some of the fuel is used in the combustion so I dont know how much pressure the return line would see but it would need to return enough fuel to keep the tank level even. That probably means that the flow rate of the pump is roughly equal to the flow rate of the return.

If your plan was to feed and return to the same tank then you might run into an issue where the two dissimilar sized tanks would try and normalize their volumes. So if you have a 20 gallon rear and a 16 gallon front, they would try and normalize to 18 gallons each. This would be heavily dependent on where you end up parking the truck for instance. If you park facing downhill for example, the rear tank would gravity feed more fuel into the front tank. That would get worse based on the grade. If both tanks were close to full then the front tank could overflow.

Alternatively, if you were to seal off one tank completely, I believe you could plumb the feed from one tank (lets say the rear) and the return to the other tank (midship). Then you just need to connect the two tanks with a hose that can exceed the gph of the lift pump. Thats kind of alot of work though, and having several feet of diesel fuel hose in that diameter is somewhat expensive. Not only that but you would have to figure out a way to attach a coupling to the tanks which would likely involve welding a fitting on them that would compromise the internal lining of the tanks and be susceptible to corrosion both inside and out.

You might be better off picking up the larger rear tank and removing the midship tank and then figuring out how to relocate the spare wheel to where the mid tank was.

 

[Old Goat]

I think it would work IF you used a big enough line. Like Kdo said, it would overflow one of the tanks. Look at semis. At least some of them do this, but they use a MUCH larger line than 5/16". It's probably 1" or bigger.

The tanks are on the sides of the truck, with the coming out of the bottom
or the end of the tanks. The line was to equalize the fuel level.
One problem we had one time, if the truck was parked on a slope, fuel would
cross over to the lower tank and leak out the vent.
The tank did have a valve to shut off the cross flow.
Yeah the cross flow was probably 1".

Goat

 

[u2slow]

I'm happy with my fuel capacity, so an aftermarket larger tank that would displace my spare tire isn't something I'm interested in. I always have a 12 foot camper on...

My Dad had a camper like that, and the stock spare location under these was too miserable to extract a tire from. He got some bracket to hold the tire on the front of the truck. With the tire gone from under there, he had a shop build a proper frame extension for 10k# towing. A little better planning and he could have had an extra fuel tank in there too.