Hey Guys, I'm thinking about installing an extra fuel tank into my suburban. Body is off the frame right now, so installation shouldn't be too bad.
Diagram attached. I've never set up a fuel tank before, so it would be great to hear what you guys think.
There are a couple things that might be less conventional, but hopefully ok:
-Using the stock mechanical fuel pump (235 engine) while adding a return line. Hoping this will get rid of vapor lock... last summer i could see gas boiling in my filter bowl by the carb. Stock pump supposedly flows at least 25gallons per hour, seems like that could happen through a 3/16 return line? 235 engine itself not expected to use more than 6gph.
-filler cap on the door step inside cab. Probably against rules in other states... but I can't think of any way it would be dangerous? As long as it's a sealed type of cap i think it's safe? Alternative is to cut a filler hole on the outside of the truck, or run a 3' filler line teeing to original filler on other side.
The factory tank mounts between the frame and drive shaft on the passenger side. If you mount the tank outside the frame rail you have a T-bone crash issue. If you mount it behind the rear where the spare is you have a hard time putting the filler outside the cab area. There aren't any great locations for an Aux tank...
If you run a return line, how do plan on returning equal parts to both tanks? You could to do as the OEMs did, use a fuel diverter valve and run off one tank then switch to the other.
Diesels trucks have both tanks plumbed together, so the level in each is always equal. This would let you simplify the return plumbing and supply hoses. If the connecting line was big enough, you could fill both tanks from stock location, assuming they are mounted at equal hight. This would also let you use only one sending unit for the fuel gauge.
I am thinking about having the return go to the aux tank, and then have a small overflow line to the main tank. The selector valve will only be for selecting which tank the pump draws on.
As for filling, I am leaning towards a second fill neck (with sealed cap) that comes through the side of the doorstep just inside the driver door.
Originally Posted by Joe H
Diesels trucks have both tanks plumbed together, so the level in each is always equal. This would let you simplify the return plumbing and supply hoses. If the connecting line was big enough, you could fill both tanks from stock location, assuming they are mounted at equal hight. This would also let you use only one sending unit for the fuel gauge.
I like the idea of plumbing the tanks together, but am worried about the connector line being low to the ground and susceptible to damage. Maybe there's a work around? How big is the connector line on the diesel trucks you're thinking of? Is it ok to route it from the bottom of the tanks, but then up and over the frame? kind of like this: O_︹_O
Joe has me thinking about trying to equalize tank levels... that way i wouldn't need selector valve.
Here are some picture ideas for how to run a level equalizing line? Seems like it wouldn't need to be a huge line, maybe a 5/16? [img]https://imgur.com/hqv1Rcf[/img]
The only variations i need to still think about: 1) connect fuel pump suction line to crossover line 2) ... or connect return to crossover instead 3) don't connect anything to the crossover
I'm leaning towards hooking the return line to crossover just in case it gets bubbles when tanks run low and start sloshing
The main tank does not have a positive vent,... so I'll probably have to drill a little hole in it's fill cap, and then put a vent line on the aux tank to make sure there's no pressure difference.
The "self-priming" equalizing line in your bottom picture won't work. It can't self prime unless the level in one tank is a bit above the top of the line. Unless the equalizing line is always below the bottom of the tanks. And even then, the draw will tend to empty one tank over the other unless the line length and everything else that causes restriction in the draw lines is equal (which isn't going to happen.) I think you will need a selector valve. I built two saddle tanks for a '72 Chevy PU I had and used a 3-way selector valve. Really pretty easy. Unless you forget to refill the inactive tanks and switch from a tank that runs dry to another empty tank. But on your vent line, and easy way to deal with that is to connect a tube between the two fill pipes that's above the level of gas in the tanks.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
Many years ago we did a 52 Suburban with a Lincoln IRS which required taking a 2 gallon notch off the top rear of the factory tank. This cut it down to 16g so we mounted a 10g reserve tank on the drivers side with an electric fuel pump and a line over to the main tank. If the main tank was allowed to get to 1/4 or lower the reserve could not overflow the main tank. An IRS center section mounts rigid to the frame so the driveshaft does not move other than spinning so everything like exhaust, lines, wires etc can be very close to the driveshaft which was necessary in this install. Been working for at least 10 years.
The "self-priming" equalizing line in your bottom picture won't work. It can't self prime unless the level in one tank is a bit above the top of the line. Unless the equalizing line is always below the bottom of the tanks. And even then, the draw will tend to empty one tank over the other unless the line length and everything else that causes restriction in the draw lines is equal (which isn't going to happen.) I think you will need a selector valve. I built two saddle tanks for a '72 Chevy PU I had and used a 3-way selector valve. Really pretty easy. Unless you forget to refill the inactive tanks and switch from a tank that runs dry to another empty tank. But on your vent line, and easy way to deal with that is to connect a tube between the two fill pipes that's above the level of gas in the tanks.
I'm with you on the lower picture... it would probably get messed up by sloshing when the tanks get low.
Your inter-tank vent line idea is pretty interesting... a good way to equalize pressure without letting the fumes out. Perhaps also good place to put a charcoal canister to prevent pressure buildup?
I'm still hoping to get away without a selector valve assuming that the 'siphon equalizing line' is effective and am leaning towards feeding the pump from main tank only (which will be a bit lower) but i agree that having the valve (or a crossfeed pump) would be safer to have one in case the crossover siphon fails.
Originally Posted by coilover
Many years ago we did a 52 Suburban with a Lincoln IRS which required taking a 2 gallon notch off the top rear of the factory tank. This cut it down to 16g so we mounted a 10g reserve tank on the drivers side with an electric fuel pump and a line over to the main tank. If the main tank was allowed to get to 1/4 or lower the reserve could not overflow the main tank. An IRS center section mounts rigid to the frame so the driveshaft does not move other than spinning so everything like exhaust, lines, wires etc can be very close to the driveshaft which was necessary in this install. Been working for at least 10 years.
That sounds like a really interesting build... I'd like to feel the ride in an IRS burb!
Here are final (hopefully) thoughts on equalizing dual fuel tank levels:
Routing the return line to the equalizer siphon line as I was planning (first picture below) is probably a bad idea on a carburated engine such as mine -if I shut off the engine when float bowl valve is open, then the return line would be able to drain via gravity into the tanks -next time i turn on the engine, a giant bubble will get pumped into the level equalizing line and interrupt the siphon -this could be solved by running the equalizer from the base of each tank, but I'm worried about low hanging fuel lines and would like to do it through a top pickup tube
Since the return line seems like a less reliable way to keep the siphon line primed I am going to take Kevin's recommendation from a couple posts back and add a selector valve -with a left-right-both selector valve I hope to normally pump from both tanks simultaneously -return line will go to just one tank -if selector valve is on 'both' then the siphon effect should equalize tank levels -if selector is switched to one tank only, then return line will fill one tank only -in that case fuel may have to overflow into the other tank via the vent line (second picture) -i should probably run a fuel sender in each tank
My otherwise stock K3500 diesel has an aftermarket auxiliary tank. Electric 6 port selector valve shifts both the supply and return to the tank you select.
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To save a lot of problem with the return line and which tank to send it to, just dump the returned fuel back into the feed line by the tanks. It will recirculate the fuel without filling either tank, and being back away from the pump, it should have time to cool off. I would think you are going to need a regulator at the carb to regulate how much fuel returns and how much is going to the carburetor.
Here are some links to fuel regulators and how they are plumbed. The first one is a vacuum operated type which would work good for you. They return more with high vacuum and less when vacuum drops like under a load.
To save a lot of problem with the return line and which tank to send it to, just dump the returned fuel back into the feed line by the tanks. It will recirculate the fuel without filling either tank, and being back away from the pump, it should have time to cool off.
I like that idea a lot. Not only does it prevent fuel overflow into the vent line possibilities, it would also prevent aeration of return gas splattering down into a tank, and save me the trouble of haphazardly tapping an NPT fitting into my sender flange.
My otherwise stock K3500 diesel has an aftermarket auxiliary tank. Electric 6 port selector valve shifts both the supply and return to the tank you select.
Sounds like a solid setup. For now I'm hoping to get away with less fuel lines... though it seems like I'm planning more each day now!
No need to go to the radiator, mount it along the frame rail. My transmission cooler is under the truck, not far from the transmission, granted I don't work it very hard, but the trans has worked like a champ for the last 20 years. There is plenty of air movement under the truck if it doesn't set to low.
hmm... i just realized that i should definitely route the return back to the tanks.
The problem (i think) with returning to the feed line is: if a vapor/air bubble enters the return then it is stuck in a loop with nowhere to escape.
By returning back to the tanks, I hope that bubbles would naturally escape the return line and I won't have to worry about them entering the feed line.
I'll probably bite the bullet and add another crossover so the return can tee into both tanks.
I think you are over thinking this, glass fuel filters have air in them at all times and don't cause problems. Any fuel that vaporizes from heat, should return to a liquid when its cooled back down, and with the fuel circulating all the time, it never should get hot enough to vaporize in the first place.
That is a good point. I guess I'm also worried about how to get the air out of such a loop when i initially fill it with fuel. Notorious over-thinker here it really impedes progress sometimes
it really impedes progress sometimes