Fuel tank issues
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From: Longview WA
Fuel tank issues
Alright I'm a little baffled 81 f250 dual tanks both brand new , the front tank is syphoning fuel from the rear and re filling itself...how? I have no overflow line connecting the 2.. shouldn't the fuel switch shut off one tank and open the other line?
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From: Wolfsburg
I have the same set up. The fuel line from the tanks both run to the switching valve located on the inside of your driver side frame rail. There the switching valve either allows the mechanical fuel pump to draw from the rear or the front tank. It sounds like your switching valve is the problem if the fuel lines are connected like stock. Are you sure you are drawing from the front tank and not the rear? The valve might be stuck on the rear tank even though the switch in the cab is on front.
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From: Angier, NC
Gunner, you did not post what motor your truck has as this may make a difference I think.
Tim is right on where the valve is, inside the left side frame rail.
The one he talks of and like I have on my 81 with a 300 six is really simple valve.
It has a hose from each tank going in and 1 going out to the pump on the motor and as far as I know this type can not fill the other tank.
If the valve goes bad it will pull fuel from only 1 tank.
If you have in tank electric fuel pumps and the valve on the frame rail has more than the 3 lines going to it then yes 1 tank can fill the other.
So what valve do you have 3 port or 6 port?
Dave ----
Tim is right on where the valve is, inside the left side frame rail.
The one he talks of and like I have on my 81 with a 300 six is really simple valve.
It has a hose from each tank going in and 1 going out to the pump on the motor and as far as I know this type can not fill the other tank.
If the valve goes bad it will pull fuel from only 1 tank.
If you have in tank electric fuel pumps and the valve on the frame rail has more than the 3 lines going to it then yes 1 tank can fill the other.
So what valve do you have 3 port or 6 port?
Dave ----
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From: Wolfsburg
Does it happen regularly?
It would be interesting to conduct a test to see if it's actually transferring or the gauges are just being weird. Drive on the front tank for a while, then let it sit and once it shows full drive to the gas station and try to fill it up. If it is indeed full, then we have a magic truck. If not it is just the amazing fuel gauges.
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From: Longview WA
Just came back from the fuel station front tank is full rear was 14.4 gallons low...it was parked nose downhill...so is that valve getting stuck and allowing fuel to be sucked into the other tank?
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From: Wolfsburg
I am really baffled. I guess that is the reason you started this thread... I am not so sure of the inner workings of the valve. I believe it is a shuttle type with a solenoid pulling it up. (Someone please correct me if I am wrong) So if the fuel is flowing from one tank to another the fuel must either flow around the shuttle or it could be stuck in a position where the through-hole lines up halfway with both inlets If that is possible. So either way, the switching valve must be at fault since there is no fuel return line that is the only place the two tanks meet. I am at a loss on how to fix that other than replacing it, but maybe the other guys have more ideas.
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From: Angier, NC
I am really baffled. I guess that is the reason you started this thread... I am not so sure of the inner workings of the valve. I believe it is a shuttle type with a solenoid pulling it up. (Someone please correct me if I am wrong) So if the fuel is flowing from one tank to another the fuel must either flow around the shuttle or it could be stuck in a position where the through-hole lines up halfway with both inlets If that is possible. So either way, the switching valve must be at fault since there is no fuel return line that is the only place the two tanks meet. I am at a loss on how to fix that other than replacing it, but maybe the other guys have more ideas.
Put power to the valve and the front tank is then used.
Could it be stuck so both the front & rear supply ports are open a little and being parked nose down then maybe the fuel is just seaking a level?
Could you park it tail down and see if the gas goes the other way?
BTW I also have that 3 port valve on my 81 flare side, added by me from a 81 style side parts truck so I have 2 tanks.
Dave ----
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From: Wolfsburg
Again you are right it is a shuttle valve. IIRC no power to the valve the rear tank is the one being used.
Put power to the valve and the front tank is then used.
Could it be stuck so both the front & rear supply ports are open a little and being parked nose down then maybe the fuel is just seaking a level?
Could you park it tail down and see if the gas goes the other way?
BTW I also have that 3 port valve on my 81 flare side, added by me from a 81 style side parts truck so I have 2 tanks.
Dave ----
Put power to the valve and the front tank is then used.
Could it be stuck so both the front & rear supply ports are open a little and being parked nose down then maybe the fuel is just seaking a level?
Could you park it tail down and see if the gas goes the other way?
BTW I also have that 3 port valve on my 81 flare side, added by me from a 81 style side parts truck so I have 2 tanks.
Dave ----
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From: Longview WA
But wait there's more.... apparently sitting with both tanks full...the truck decided the front tank needs the rear tanks fuel...I got gas spewing all over out of the fill hole when I removed the cap...
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From: Angier, NC
Dave ----
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On my '84, power to the valve draws fuel from the front tank. No power draws fuel from the rear. I learned this the hard way when the fuse worked loose. (Never let the parking brake slam when you release it!!!) I had the switch set to the front tank, but the gauge never dropped and fuel was drawn from the rear (default) tank.
Since then, I've always drawn down the front tank first in case the valve ever fails. I don't want to get stranded somewhere with an empty rear tank and a full front tank I can't use.
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From: Virginia
Why would the fuel want to go from one tank to the other? Is your venting system clogged or has it been plugged off? You should have a vent on the top of each tank, and they run over to the passenger side frame rail,, and run up front to the charcoal canister.
Tuned
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From: East Tennessee
I had to install a new rear tank a couple of years ago and that had happened to me. Filled both tanks and drove it home running on the new rear tank. Next day I was in the garage and smelled gas. I thought oh boy what now. I discovered the front tank was pouring gas out the filler neck. After checking into it the return line to the rear tank was stopped up so all the gas returning was forced into the front tank. Cleaned out the line and it started working right again.