Dual Tanks - 3500

mkjj123 · January 6, 2006

We have a 2004 3500 with dual gas tanks. It seems that noone (dealer, mechanics) can tell us how the tanks actually feed the engine. Do they feed equally, in that if both are filled they should empty at about the same rate? Will it cause a problem if one is filled and the other is let run dry? Does the fuel system require that each tank have fuel?

We typically fill each tank equally; same # gallons in each, or fill both at the same time. This is probably the best thing to do but it would be nice if we knew what was actually going on in there.

Any insight on this would be greatly appreciated.

Regards

GM-Tech · January 6, 2006

I don't have the numbers in front of me but it works this way. First, when you fill the tank(s), it is filling both at the same time. If you have the type of truck that actually has two filler necks, which sounds like may be the case based on what you said, then none of the following applies.

The auxillary (rear) tank has a transfer pump that pumps fuel into the main tank. This occurs based on the percentage of fuel in each tank (each has its own level sensor).

The engine is fed only by the primary (side) tank's fuel pump, just like in single tank setups. Nothing different there.

If you have two filler necks, I'd have to look for a description and operation. We don't see those. Not sure how it works or if it even comes from GM that way (I'm guessing it does).

mkjj123 · January 6, 2006

Yes, each tank has its own filler. Oddly there is only a single fuel guage that seems to report the total fuel of the two tanks combined. For instance, if I were to fill one tank and leave the other empty, the guage would read about half full.

Thanks for the quick reply. If you're able to get any info on this configuration, I'd love to hear about it.

Have a good weekend.

99silveradoz71 · January 8, 2006

hmm, that's odd. You'd think with dual fill necks that you'd have a toggle switch to choose a tank.

GM-Tech · January 8, 2006

I've seen the dual fillers on the cab&chassis where they add a dump bed or stake bed or something like that, but I've never worked on one. I'm guessing it works the same way as the smaller trucks with auxillary tanks and a single filler. In other words, the aux. tank has a transfer pump that keeps transferring fuel to the main tank.