Just found 3rd tank on truck...stock?

[Claidig]

New owner here (started one other newbie thread) but I just wanted to ask why my truck would have 3 gas tanks? I didn't even realize there was another one stuck under the bed on the drivers side until I was checking for rust? I checked and the tank selector under my seat does have 3 tank choices...RR LL and MM (and off). Not sure what those stand for yet either.

Was this an option from the factory? and if so does it possibly help determine what trim level I have...like Custom Camper?

I would like to buy some emblems but not sure which ones I need yet so maybe this can help.
Thanks.

[SS Tim]

Pictures always help, but I found yours on another post. The stock tank would be behind the seat in the cab. A factory installed optional tank would be installed on the drivers side under the bed with a filler going up through the bed and out the side. It will also have a selector switch on the far left dash near the door. Saddle/Aux. tanks were offered both as a GM accessory to be dealer installed or aftermarket and there are many variations. Some have doors cut in the bedside to access the filler and others had the filler in the wheel well that often as not has a can over the top to keep, er... stuff out of the tank during fueling. Most mounted under the bed, some were inside the bed forward of the wheel wells. Generally all the aftermarket installations used a manual selector valve on the floor. It was cheap, functional and universal. The method of operation was to fill the saddle tanks and drive them dry then switch to the factory tank last as generally it was the only one with a gauge.
These were often installed on campers to get past the slingshot range due to sometimes single digit gas mileage in an generally overloaded camper truck.

Looks like your system might be a combination of parts. LL is likely left tank. RR right and MM cab tank. Best thing to do is chase down and draw out your plumbing from the valve. Don't move the selector around until you know the tanks and lines are clean. Many times these tanks fall into disuse and nothing remaining inside should ever go through a carb.

[Spaz]

I have the same setup on my truck. Ill be yanking out the two side tanks and possibly selling em. The previous owner used the regular in cab tank. Anyone know where i can find the filler panels to weld in or do i have to change out the bed side?
Posted via Mobile Device

[special-K]

Originally Posted by Spaz

I have the same setup on my truck. Ill be yanking out the two side tanks and possibly selling em. The previous owner used the regular in cab tank. Anyone know where i can find the filler panels to weld in or do i have to change out the bed side?
Posted via Mobile Device

Cut pieces of body metal from a hood or whatever and weld them in.

[GASoline71]

My truck ('72 GMC)had the sidesaddle auxilliary tanks mounted as a dealer option. They were removed by the PO. But I have holes in the bedsides and through the bed floor for the filler necks. Also a spot on the floor in the cab where a selector switch was mounted near the drivers side of the bench seat.

Gary