# 2000 K3500 dual tanks not using both tanks



## bgingras (Jan 16, 2004)

I got a good one...I ran out of gas! but I didn't...the truck is a 2000 chevy 3500 C+C. It has dual tanks. When you fill only the front it usually reads 1/2 full, when both tanks are fll it Reads full...as long as the front tank is full it's supposed to use the rear tank first...well it's still reading full when both are full and half when the front is empty as it runs dry and stalls...it's not using the rear tank all. I'm guessing that something is stuck? where is the fuel selector? I'm confused.


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## carlriv2 (Oct 15, 2001)

fuel transfer pump is bad. It is along the inside of the drivers side frame rail by the rear wheels. This pump moves the fuel from the rear tank to the front tank. I had a 1999 and replaced it 3 or 4 times


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## bgingras (Jan 16, 2004)

thanks, just discovered that it had this pump on the rail...now I just have to find one ASAP...we have snow on the way!


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## bgingras (Jan 16, 2004)

well I replaced the pump...now a bigger problem, as soon as I fired up the truck it started spraying fuel, the entire top of the sending unit on the rear tank is rotted through...there should be a recall for this one, who designs these things?!?! The tanks has a 6" deep bowl where the sending until goes, no wonder it willed up with salt and sand and water and rotted through. Does anyone know the part number for this rear sending unit?


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## carlriv2 (Oct 15, 2001)

I dont, but I think its big money. I would disconnect the transfer pump and run the truck for the weekend from the front tank only.


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## bgingras (Jan 16, 2004)

I disconnected the new pump and took the plug from the old one, taped it and plugged it into the harness so no dirt got in it. The rear sending until does not have a pump on board so it "should" be cheaper...man this thing is starting to come apart faster than I can keep up...it just hit 70K and so far an alternator, fuel pump, brakes after 12K miles, and now the sending unit all in 2 weeks time...plus I have a shimmy from the front end that appears to be from a bad steering stabilizer, oh and an oil leak from one of the cooling lines, plus the coolant is starting to "disappear"


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## B&B (Nov 4, 2006)

Your gonna need to replace the front sender too for the system to work properly. The way this setup works is theres a "fuel balance module" on the frame rail that monitors the fuel level in the tanks.When the front tank gets down to about 1/4 full the fuel balance module turns on the frame rail mounted transfer pump (the pump you replaced) and begins to pump the fuel from the rear tank into the front one. If the front sender never reads under a 1/2 tank, which you said it doesn't, then the balance module wont turn on the fuel pump and transfer the fuel to the front tank since it doesn't know it's empty. Hope this helps.


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## bgingras (Jan 16, 2004)

this truck has always used the rear first...the rear tank always was the empty one, then the front went down..are you saying that it hasn't worked right for the 2 years we have had it? It did start pumping yesterday the minute I started the truck, only trouble is that is sprayed from the rotted line right away.


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## carlriv2 (Oct 15, 2001)

I think you will be ok just changing the rear. Thats what we did. The gauge reads 1/2 tank because you have 1/2 the gas. The rear tank is full and the front tank is empty, but you have no way of getting the gas out of the rear tank. The engine will be out of fuel when the gauge reads 1/2 because that 1/2 tank is not available to the engine. If my memory is correct we could only get a dealer part and it was $400 plus.

Did you get plowable snow last night? We did a couple of walks and shady areas at a building that runs 3 shifts.


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## bgingras (Jan 16, 2004)

no snow on the ground at 7am, and I think I found a sender for $150 from autozone.


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## B&B (Nov 4, 2006)

Did you pull the sender out of the tank yet? Does it have a pump *inside* the sender? Some do and some don't as there were a couple different configurations with these duel tank set ups and the configuration I described in my first post is the most common style.


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## bgingras (Jan 16, 2004)

I'm not pulling it until I have a new one, but there should not be a pump in the tank as there was the frame mounted pump(redundant) and it only has a 2 wire connector, and 2 wires will not run both a pump and a level indicator.

What I'm getting is the just under half on the gauge showing the fact that the front(larger tank) is empty and the rear is full. Now the real question is how contaminated is the rear tank...with the kind of holes I found in the lines, I suspect we have water and road slat in the tank. Does anyone know how to dispose of that much contaminated fuel?On the upside I don't have to remove the tank to work on, simply raising the bed gives me full access. Again, they really need to fix this issue of a 6" deep bowl for water and sand/salt to collect around the sending unit, just a really stupid design IMHO.


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