I have installed an auxiliary tank. It feeds through the filler tube. The problem is my main fuel tank cap shuts off ALL the air not letting the fuel drain from the auxiliary tank. It works fine if I leave the cap off...which is not feasible. Can anybody offer some help.

Thanks, Tony

 

I have three tanks on my truck and I would NEVER hook one up to drain into the factory tank; that is just a recipe for a big fuel-spill disaster and could land you with a big fine, should it happen in front of the wrong witnesses.


The ONLY way to plumb in extra tanks is through top-of-tank draw-straws and MANUAL tank-selector valves.


I have seen and read of all kinds of gimmicky auxilliary tank set-ups that are just problems waiting to happen.


Do it right and it will be an asset for years to come.

 

I have a 70 gal. in-bed tank that feeds and returns out the top and I switch between it and the factory tank with a Pollak 6-port electric valve. I'm not comfortable with the idea of bottom feed but that's up to you.

 

Most of the big trucks that I am familiar with have "saddle-tanks", usually one on each side and sometimes two on each side.

Fuel is drawn from only one tank, with equalizers running from each tank bottom such that the fuel in all tanks seeks the same level.

A very common problem with them is, when all tanks are nearly full and the truck is not level for more than a few minutes, the fuel from the higher tanks pushes out the vents of the lower tanks.

They fix this problem by incorporating shut-off valves in the lines between the tanks; when the tanks are all full, the valves are all closed; then, when the main DRAW tank is nearing EMPTY, the valves are opened, letting the FULL tank(s) increase the level of the main tank.


This set-up works for them because all the tanks are on the same level.


Trying to utilize a similar system when one tank is above/higher than another, without extreme vigilance, will sooner or later result in all the fuel from the higher tank being on the ground.

 

drill a small hole in the diesel cap on the filler tube on the stock tank... call it done!

 

I would do a seperate feed from your extra tank with a pollak style valve. I have a 110 gal bed tank but its not plumbed in. I just have a filler nozzle and pump and fill up as needed. That thing that goes in the filler neck just seems like a fuel spill waiting to happen.

 

Your vent is plugged. There are several ports on top of the sending unit, one of which is a vent. I installed a piece of tubing leading to a small filter on the tank vent and vented my cap as well. Cheap insurance.

 

Thanks Man! The way it is right now it is sealed tight as a drum. I'll look and see if I can find the vent.

Tony

 

You'll probably need to clean it out first. Use a small piece of stiff wire to unplug it, rinse with a shot of WD40 and blow it clean with some compressed air. Then the tubing to a filter trick will keep it open forever after that. I just stuffed some cotton in the end of the tubing.

 

If the aux. tank is mounted in the box, it will gravity feed the main tank until it is full, then push the rest out the hole in the cap.

 

It's gotta be vented somewhere. Choose your preferred leak location.

 

This is true. I have an on/off valve inside the truck, so it is not "JUST" a gravity feed. The problem is that nothing can drain into the tank at all. I let is set overnight, and nothing drained into the tank.

Thanks for the help, Tony

 

You might be able to crack it open and let it drain for a few hours on a long trip with no worries, depending on how big the aux tank is and how much control you have with the valve.

But that would need to be a carefully monitored learning experience.

 

The only "solution" I can see for this is to drill a hole in the top of the main tank and add a vent on a hose that runs up past the top of the auxiliary tank. All other vents and holes in the top of the main tank, as well as its filler cap, must be permanently sealed up. You need to think of these two tanks joined together as being one big tank now. You wouldn't drill a hole half way up a tank for a vent, you'd drill it at the top.

 

Well, I have been conceiving a custom bed solution for a while, one of the design features is going to be a ~100 gal tank in between the frame rails. Part of my design is going to involve elevating the bed of the truck up to almost rear-window height, so I'll have plenty of extra room for it. And I will be replacing the factory fuel tank with my custom tank. You might want to consider something similar.

Double tanks = double trouble. Tank selector valves are a constant headache and they go bad. I had a Ford E-350 van with dual tanks. One fine, hot Texas day I was somewhere on I-45 heading back up from Houston and happened to glance out the side mirror and noticed that suddenly I was leaving a huge trail of gasoline behind me. I stopped, got out and saw that there was gas shooting out of the filler cap of the front tank. I had selected the rear tank, plan was to run it down to 1/4 then run the front tank down to 1/4 and refuel. Front tank was 18 gallons and rear was 22. What was happening was the selector valve was stuck in the middle, it was pumping fuel not just to the engine but also pressurizing the front tank using the gas from the back tank.

Luckily, I was able to switch to the front tank and when it was almost empty, I switched to the rear tank again (which was very soon empty - cause it had put all the fuel in the front tank) and then back to the front tank. So after that, could only use the front tank. I never did fix that issue, I sold the van and let it be the next guy's problem.