87 chevy dual fuel tank help

rugy04 · 11-10-2007, 12:13 PM

Hey folks, I recently purchased an old 1987 chevy shortbox,not much experience with pickups so forgive my ignorance.
It has dual fuel tanks but only one filler door, I haven't gotten under it to look closer but it looks to be connected, could this be?
It will only run on one tank, and when I go to fill it with fuel it will only take fuel VERY slowly, takes forever to fill that one tank!!
Is it possible there is a valve and solinoid that controls both tanks, sort of like a butterfly valve to direct the fuel when filling, or is the box from a different truck and the one tank is disengaged somehow, it sure looks to be hooked together and to me it would not make sense that if they were seperate and one tank is disabled why is there a filling problem?
Would really appreciate any info on this!
THANKS!

crabtruck · 11-10-2007, 02:25 PM

Welcome to the forum rugy04, congrats on the truck.
Any chance of getting some pics on this? Hard to tell what's "remodeled" without seeing it.
Is there a switch for the tanks ? How much does your gauge move for 10 or 15 gallons used ?
Slow filling (assuming you mean pump shuts off if you try to fill to fast) could be due to a restriction.
But could be either home plumbing of a second tank or neck may have a tip upwards and that would trip the pump off.
Does it have a hose from door down that is twisted or folded/collapsed ?
Have you looked at the gas lines to see where they join for use ?
Typically there is a "block" with lines to engine and twin sets coming off to tanks,
could be where cab and bed meet in the middle, has wires also.
Have you figured out how much gas you are able to fill total and then how big are the tanks?
If you don't know how many gallons it's easy to calc by dimensions.

GMC004DOOR · 11-10-2007, 02:59 PM

easyst way: how many gal of gas is it to fill it?

rugy04 · 11-11-2007, 06:35 AM

I'm not sure of the exact capacity of the tanks but the left side seems to be aroun 14 Gal.
There is a rocker switch for the tanks ( activate Left or Right )
your standard factory switch but the truck will not run when activated to the Right tank, there is fuel in the tank but when I switch back and forth the fuel gauge does not move to indicate the ammount in the right side, but it will when on the left tank position.
There is no visible restriction to the fill tubes, the two tanks are connected by a larger, looks to be a 2 inch hose with y fitting to branch off into the top of each tank, and a smaller looks to be maybe a 3/4 hose that also branches off into the top of each tank.
There is a Block so to speak, that looks to be like a solinoid and juction for the lines in, it is located along side the front of the right hand side tank.
It all looks to be factory but I guess I did not know if there was such a thing as dual tanks, that are linked together with one fill tube, having to fill both tanks from one fill tube, thats why I was thinking that there might be a butterfly valve in that line somewhere that might be activated by the rocker switch somehow,to designate which tank is being filled and also which tank it is drawing from.
Any info is much appreciated, Thanks

crabtruck · 11-11-2007, 11:55 PM

Regardless of how gas gets in tank, its probably getting out in a traditional way.
See if the diagram in this other thread is any help.
Wiring Harness

rugy04 · 11-13-2007, 04:09 PM

I guess one of the things I would like to know is if any one has ever heard of a system where both tanks are filled from the same filler neck,( only one door ) ? If so how does it work? ( what directs the fuel into designated tank) I do noe see any sign of a valve or any wires to supply energy to a valve anywhere on the fill line.

Dragonfly · 01-26-2008, 11:10 AM

Actually an 87 should have an electric fuel pump in the tank and a computer. Unless they put an older engine in with a mechanical fuel pump and by passed the computer.

If your truck was originally designed for dual tanks there will be a switch by the ash tray to select the tank. There should also be a electric selenoid/valve on the passenger side right frame just behind the cab or just under the front of the box. You should also have two fuel filler doors, one on the left and one on the right.
It sounds like someone put a box (without dual tank access) on a truck with dual tanks or added a tank on the right (passenger) side of a truck that was not set up for dual tanks from the factory. I suspect the latter of the the two options.
You cannot successfully fill two tanks by splitting off the filler neck to each one. One will have to be filled before the other will accept fuel. By the time that happens the full one will be more than over filled and cause other problems for you.
You would also have to split the fuel lines into one supply line for the carb. Without a switching valve you would end up sucking air out of the empty tank while trying to suck fuel from the full tank. Essentially you would have to keep fuel in both tanks to avoid this issue, one of them could never be truly empty.

Dragonfly · 01-27-2008, 12:06 PM

After going back and re-reading your post it's apperant someone put a different box on your truck without dual tank access. You have the factory setup for dual tanks, i.e. the switch and the seleniod. With the key "on" and engine-fan-radio off, can you hear the seleniod switch over when you move the switch? You should be able to hear it buzz for a few seconds. If it's not switching over then the seleniod is bad. I would say that's probably why you can't run it on the other tank and you don't get a reading on the fuel gauge. They are around $90 for a new one

11-10-2007, 12:13 PM	#1
rugy04 Junior Member Join Date: Nov 2007 Posts: 3	87 chevy dual fuel tank help Hey folks, I recently purchased an old 1987 chevy shortbox,not much experience with pickups so forgive my ignorance. It has dual fuel tanks but only one filler door, I haven't gotten under it to look closer but it looks to be connected, could this be? It will only run on one tank, and when I go to fill it with fuel it will only take fuel VERY slowly, takes forever to fill that one tank!! Is it possible there is a valve and solinoid that controls both tanks, sort of like a butterfly valve to direct the fuel when filling, or is the box from a different truck and the one tank is disengaged somehow, it sure looks to be hooked together and to me it would not make sense that if they were seperate and one tank is disabled why is there a filling problem? Would really appreciate any info on this! THANKS!

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11-10-2007, 02:25 PM	#2
crabtruck Senior Member Join Date: Jul 2007 Posts: 4,107	Welcome to the forum rugy04, congrats on the truck. Any chance of getting some pics on this? Hard to tell what's "remodeled" without seeing it. Is there a switch for the tanks ? How much does your gauge move for 10 or 15 gallons used ? Slow filling (assuming you mean pump shuts off if you try to fill to fast) could be due to a restriction. But could be either home plumbing of a second tank or neck may have a tip upwards and that would trip the pump off. Does it have a hose from door down that is twisted or folded/collapsed ? Have you looked at the gas lines to see where they join for use ? Typically there is a "block" with lines to engine and twin sets coming off to tanks, could be where cab and bed meet in the middle, has wires also. Have you figured out how much gas you are able to fill total and then how big are the tanks? If you don't know how many gallons it's easy to calc by dimensions.

11-10-2007, 02:59 PM	#3
GMC004DOOR Full Member Join Date: Oct 2007 Posts: 27	easyst way: how many gal of gas is it to fill it?

11-11-2007, 06:35 AM	#4
rugy04 Junior Member Join Date: Nov 2007 Posts: 3	I'm not sure of the exact capacity of the tanks but the left side seems to be aroun 14 Gal. There is a rocker switch for the tanks ( activate Left or Right ) your standard factory switch but the truck will not run when activated to the Right tank, there is fuel in the tank but when I switch back and forth the fuel gauge does not move to indicate the ammount in the right side, but it will when on the left tank position. There is no visible restriction to the fill tubes, the two tanks are connected by a larger, looks to be a 2 inch hose with y fitting to branch off into the top of each tank, and a smaller looks to be maybe a 3/4 hose that also branches off into the top of each tank. There is a Block so to speak, that looks to be like a solinoid and juction for the lines in, it is located along side the front of the right hand side tank. It all looks to be factory but I guess I did not know if there was such a thing as dual tanks, that are linked together with one fill tube, having to fill both tanks from one fill tube, thats why I was thinking that there might be a butterfly valve in that line somewhere that might be activated by the rocker switch somehow,to designate which tank is being filled and also which tank it is drawing from. Any info is much appreciated, Thanks

11-11-2007, 11:55 PM	#5
crabtruck Senior Member Join Date: Jul 2007 Posts: 4,107	Regardless of how gas gets in tank, its probably getting out in a traditional way. See if the diagram in this other thread is any help. Wiring Harness

11-13-2007, 04:09 PM	#6
rugy04 Junior Member Join Date: Nov 2007 Posts: 3	I guess one of the things I would like to know is if any one has ever heard of a system where both tanks are filled from the same filler neck,( only one door ) ? If so how does it work? ( what directs the fuel into designated tank) I do noe see any sign of a valve or any wires to supply energy to a valve anywhere on the fill line.

01-26-2008, 11:10 AM	#7
Dragonfly Full Member Join Date: Jan 2008 Posts: 19	Actually an 87 should have an electric fuel pump in the tank and a computer. Unless they put an older engine in with a mechanical fuel pump and by passed the computer. If your truck was originally designed for dual tanks there will be a switch by the ash tray to select the tank. There should also be a electric selenoid/valve on the passenger side right frame just behind the cab or just under the front of the box. You should also have two fuel filler doors, one on the left and one on the right. It sounds like someone put a box (without dual tank access) on a truck with dual tanks or added a tank on the right (passenger) side of a truck that was not set up for dual tanks from the factory. I suspect the latter of the the two options. You cannot successfully fill two tanks by splitting off the filler neck to each one. One will have to be filled before the other will accept fuel. By the time that happens the full one will be more than over filled and cause other problems for you. You would also have to split the fuel lines into one supply line for the carb. Without a switching valve you would end up sucking air out of the empty tank while trying to suck fuel from the full tank. Essentially you would have to keep fuel in both tanks to avoid this issue, one of them could never be truly empty.

01-27-2008, 12:06 PM	#8
Dragonfly Full Member Join Date: Jan 2008 Posts: 19	After going back and re-reading your post it's apperant someone put a different box on your truck without dual tank access. You have the factory setup for dual tanks, i.e. the switch and the seleniod. With the key "on" and engine-fan-radio off, can you hear the seleniod switch over when you move the switch? You should be able to hear it buzz for a few seconds. If it's not switching over then the seleniod is bad. I would say that's probably why you can't run it on the other tank and you don't get a reading on the fuel gauge. They are around $90 for a new one