Factory Auxiliary Fuel Tanks (Option NL2)

[Andrew S]

I read all these great threads helping me out with projects, now it's time for me to give back a little technical information of my own.

My 1972 K20 was sold with the NL2 factory option, auxiliary fuel tank. This consists of a manual valve mounted in the floor next to the drivers seat, an gauge switch mounted in the dash, and ~18 gallon tank mounted on the left hand side, under the bed.

The auxiliary tank hadn't been used on my truck in quite some time, and had started to rust considerably inside. Here's the original after I pulled it out.



I also wanted to remove the in-cab tank to gain some storage room behind the seat. So, with a bit of help, I built a stainless replacement for the auxiliary tank (left hand side), and a matching one for the right hand side of the truck. This gave me the storage I wanted behind the seat, and about 36 gallons of fuel, way more than needed.






You'll need a few other parts if you're adding these tanks from scratch. Sending units/suction tubes turn up on eBay occasionally, or you can build one. You will need to sacrifice an in-tank sending unit to build you own auxiliary tank version.

Following are some details for those who might want to re-create the same thing. You can collect just about everything needed from the for sale forum here, given enough time.

Tanks are mounted through the bed, with 7/16" x 12" carriage bolts. The hole locations are shown in the factory assembly manual, as is the location of the filler neck holes.

Filler Necks:
Stock in-cab tank: 2 1/4" OD, 2 1/4" Grommet
Auxiliary Tank: 2" OD, 2 1/4" Grommet
Auxiliary tank vent line: 1/2"
Auxiliary tank filler hose: 1 3/8"
I recently saw an ad on the forum for someone who reproduced the sheet metal filler neck covers. These are the same as the Blazers, just mounted in a different location.

Manual Selector Valves:
These are still available from many marine suppliers, simply add your own fittings as needed:
http://www.westmarine.com/buy/sierra...rsal--14605331

Replacement Fuel Sender Filter Sock:
GM Part Number #5651702 (3/8” diameter)

Fuel Filler Caps:
Napa 703-1092, Stant 10742 both fit the factory auxiliary tank filler neck.
You can also use a Blazer filler neck in this area, by shortening the steel neck as needed. Blazer filler neck uses a Blazer filler cap.


I will add detailed plans for building your own tanks, and sending units over the next few days. Hope this helps out anyone considering this as an option.

Andrew

[yoncey]

This is great! I have also wanted to put back an AUX tank on both sides of the truck. Your findings...and results will get me going on doing mine!

[57taskforce]

Your timing couldn't be better, I'm picking up a 72 k20 with the nl2 option this weekend. I'll be keeping an eye on this thread! Thanks for posting this up!

[Gei-Corp]

Andrew,

Where did you find the 7/16 x 12 inch long carriage bolts. I can only find 3/8 and 1/2. I thought about maybe using a coupling nut in place of the 3.5 inch spacer under the bed and using a shorter carriage bolt with all thread coming up from the bottom.

Thx

Chris

[jocko]

Chris - welcome to the site. Note that the thread is about 2 years old, so you may want to pm Andrew. Again, welcome from a born and bred (and displaced) Hoosier.

[Andrew S]

Chris,
I still need to get this thread completed, somehow life got in the way...
I couldn't find any 7/16 carriage bolts long enough either, so I ended up lengthening shorter ones by cutting and welding a rod in the middle. Your coupling nut idea sounds like it would work fine too.
Andrew

[El Dorado Jim]

http://www.u-neacfasteners.com/ this place has all the hard to find bolts you need, I got the 14" or 16"carriage bolts I used for mounting my tanks from them.I used big flat washers and lock nuts on the bottom of the tanks...this place is near me in Sacramento.I am sure they would ship them to you

[Tdrcreyn4]

Sub

[Orange Crate]

Thanks for putting this all in one place. I have yet to reinstall my aux tank because I needed a source for the long carriage bolts. Thanks again.

[seward67]

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In post #1 Andrew posted a link to a web site that has valves.

[Tdrcreyn4]

Sub

[pilotXC]

Originally Posted by Andrew S

I read all these great threads helping me out with projects, now it's time for me to give back a little technical information of my own.

My 1972 K20 was sold with the NL2 factory option, auxiliary fuel tank. This consists of a manual valve mounted in the floor next to the drivers seat, an gauge switch mounted in the dash, and ~18 gallon tank mounted on the left hand side, under the bed.

The auxiliary tank hadn't been used on my truck in quite some time, and had started to rust considerably inside. Here's the original after I pulled it out.



I also wanted to remove the in-cab tank to gain some storage room behind the seat. So, with a bit of help, I built a stainless replacement for the auxiliary tank (left hand side), and a matching one for the right hand side of the truck. This gave me the storage I wanted behind the seat, and about 36 gallons of fuel, way more than needed.






You'll need a few other parts if you're adding these tanks from scratch. Sending units/suction tubes turn up on eBay occasionally, or you can build one. You will need to sacrifice an in-tank sending unit to build you own auxiliary tank version.

Following are some details for those who might want to re-create the same thing. You can collect just about everything needed from the for sale forum here, given enough time.

Tanks are mounted through the bed, with 7/16" x 12" carriage bolts. The hole locations are shown in the factory assembly manual, as is the location of the filler neck holes.

Filler Necks:
Stock in-cab tank: 2 1/4" OD, 2 1/4" Grommet
Auxiliary Tank: 2" OD, 2 1/4" Grommet
Auxiliary tank vent line: 1/2"
Auxiliary tank filler hose: 1 3/8"
I recently saw an ad on the forum for someone who reproduced the sheet metal filler neck covers. These are the same as the Blazers, just mounted in a different location.

Manual Selector Valves:
These are still available from many marine suppliers, simply add your own fittings as needed:
http://www.westmarine.com/buy/sierra...rsal--14605331

Replacement Fuel Sender Filter Sock:
GM Part Number #5651702 (3/8” diameter)

Fuel Filler Caps:
Napa 703-1092, Stant 10742 both fit the factory auxiliary tank filler neck.
You can also use a Blazer filler neck in this area, by shortening the steel neck as needed. Blazer filler neck uses a Blazer filler cap.


I will add detailed plans for building your own tanks, and sending units over the next few days. Hope this helps out anyone considering this as an option.

Andrew

I appreciate all this help, was hard to find a cap that would fit before I found this thread.

I got the Napa 703-1092 cap, but wanted a locking one. They were super helpful and pulled about 5 different caps that were the right diameter, but only one actually worked.

So, if you're looking for a locking cap for the factory aux tank, it's Napa Part 703-1838.