Auxiliary tank refurb

A couple months ago I was walking to my truck and noticed fluid under the rear of the truck. Closer investigation revealed the exhaust pipe had been contacting my auxiliary gas tank and had rubbed a pinhole in the corner seam. I pumped the gas out and applied some JB Weld to the hole. I decided to remove the tank and make sure the JB Weld sealed the hole. If it didn't I would probably have to weld the tank.

I also decided to do some mods to the tank while it was out. The tank was designed for a 90's GMC truck. Consequently, the vent tube makes a 90 degree bend directly towards the frame on this Ford. To clear the frame the vent hose must drop slightly. When gasoline settles in the hose it hydraulically locks the hose and the vent doesn't work well. Because of this you have to fill the tank on the pump nozzle's lowest setting. This sucks when it's cold outside. Also, the gas station I normally go to has replaced their pump nozzles with nozzles that don't have a 'slow' setting. This means I now have to stand there and manually fill the tank. It's a pain to fill the tank without the nozzle kicking off. I'm going to modify the existing vent so that there will be no low points for gas to settle.

I'm also gonna install a second vent and 'T' it into the main tank filler vent. This will help with venting while filling the tank. On very hot days the gas in the auxiliary tank will expand and run out of the filler neck. T-ing into the main tank will give more room for the auxiliary tank to expand...since the main tank has a filtered vent under the hood. Also, the new vent should provide a return in case I accidentally tried to overfill the main tank from the auxiliary tank.

The last mod I'm gonna do is to change the pump setup. I currently have an external pump which draws gas from the tank and pumps it into the main tank through the main tank fill vent hose. The lowest point I found to mount the external fuel pump is on the support for the trailer hitch. This is still well above the lowest level of the tank and it doesn't pump all the gas out of the tank that it could. I'm going to convert the tank back to an in-pump fuel pump like it originally had. In-pump fuel tanks are relatively cheap now ($40). This will also simplify things under my truck.

Here is the auxiliary tank after I removed it. Notice the vent tube in the upper left of the picture.

I cut it off to allow the vent hose to go up and over the frame. This should eliminate gas settling in the hose and interfering with venting.

I used a 1" holesaw to drill the hole for the new vent. I used a magnet to clean out the shavings that fell into the tank.

Here is the fuel bulkhead fitting...Summit Racing P/N RUS-670880. It's an AN-12 fitting which is 3/4". This should provide good venting for the tank. 'beddins' at thedieselstop.com gave me the idea.

Here is the AN to hose fitting...Summit Racing P/N AER-FCM1535. To bad these fancy fittings will be hidden.

Here is an overall view of the mods so far. The red arrow points to the modified vent tube. The white arrow points to the repair I made with JB Weld. The tank now has some gasoline in it and I'm checking to see if it will leak. I let it set for a couple days and it didn't leak.

Here is the fuel assembly. When I changed to an external pump setup I replaced the in-tank fuel pump with a piece of hose. I am now going back to an in-tank fuel pump as I think it will work better.

Another reason I got rid of the in-tank pump before was because the plastic pass-thru for the fuel pump power wire was a constant source of leaks. The bolt in the coverplate seals this hole. One of the challenges of going back to an in-tank pump is coming up with a better, leak-free way of powering the pump.

Here is the in-tank pump and...

...and pump strainer I got at AutoZone.

Here is the fuel assembly with the new fuel pump.

As I mentioned earlier, the challenge for this new setup was devising a way to get power to the pump without leaking. My friend Mike happened to stop by and suggested using a bolt pass-thru with nuts/rubber washers/gaskets sandwiched on either end with plenty of gas-safe RTV. What a good idea! Why didn't I think of that? The washers keep the power electrically isolated from the tank.

Here is the completed assembly. I crimped AND soldered all the electrical connections. Everything seems to work okay. I also decided to add a seperate ground instead of relying on the tank to ground the pump.

The fuel pump assembly is mounted in the tank, and hopefully leak-free. I don't use the return line or the emissions thingy, so I tied them together.

The tank is mounted.

The original vent hose now has no low points to collect fuel and interfere with venting.

A shot of the new vent.

I made a contraption to insert in the main fuel tank's filler vent hose. The small hose fitting is where the gas from the auxiliary fuel tanks enters. The silver hose fitting is where the new vent hose will connect.

A shot of me getting into my work.

The new fittings in place.

Here is the offending section of exhaust pipe. It took about 30 seconds with the Sawzall to remove it. I'll replace it with a section that avoids the auxiliary fuel tank.

When I finished all the plumbing I took the truck to town and filled it up. Results were mixed.

The tank patch didn't leak.
Nothing else leaked.
The pump worked like it should.

The auxiliary tank didn't fill as fast as I'd hoped. It fills faster than it did, but not fast enough to use an automatic setting on the pump nozzle. Hmmmmmmm. I guess I need to look at the filler pipe itself. It almost runs uphill a little. I need to add some downward slope to it.

Update - I filled the auxiliary tank and made sure the little flap on the main fill was opened more. This allowed the auxiliary tank to fill alot faster. It would fill on the second-to-fastest notch on the pump handle. I could feel the air coming out of the main tank filler. If I put my finger over the main tank filler hole the pump would kick off. I might remove the little flap to allow the auxiliary tank to vent easier. I'm still gonna see about adding more down slope to the auxiliary tank fill as I think this would help, too.

I made a couple more modifications to see if I can increase the flow of filling the auxiliary tank.

I made the vents larger in the main tank filler and got rid of the little flap. I didn't open up the hole completely because I still want the nozzle to rest in the hole.

While I had the filler neck out I shortened the hardline portion of the vent. This will allow me to connect the vent hose more to my liking.

Now the connections are much cleaner, and there are no low spots to hold gasoline.

I placed a shim under the auxiliary tank fill to add some slope to it. If this works I'll replace the wood shim with something more respectable.

When I get some results I'll post them here. With two full tanks of gas I only need to refill every 3-4 weeks.

Update 2/10/03 - I was able to fill the auxiliary tank on the 2nd fastest setting without the pump kicking off. I'll see how it does over the course of a few months.


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