Wanting to add a second fuel tank - help?

[OneShot]

Hi gurus,

I have a 79 c20 and it has a 16 gallon tank. I use it to drive to college and back (about 70 miles) and this tank is just barely large enough for me to get there and back in a weekend. I want to add a second tank and make it look stock (I know dual tanks was an option...). My current tank is on the passenger side. I have heard bad things about leaks and safety issues with the dual tank setup on the squarebodies. What tank should I get, and should I use the electric valve or should I just run the lines to a valve I can control in the cab?

 

[rich weyand]

The safety issue primarily relates to the tanks being located outside the frame rails. Depending on who's counting, the total number of fatalities from side-impact collisions resulting in fuel-tank fires runs from 155 to 1800, out of more than 10 million trucks sold with side-saddle tanks. Meh.

If you have a long bed, you can replace your existing 16-gallon fuel tank with a 20-gallon fuel tank with no other modifications.

If you have a short bed, you can add another 16-gallon tank on the other side. It is much easier if the second fuel door already exists on your bed. If not, you need to add a fuel filler somewhere. Several options here, including patching in a fuel-door from an existing donor truck.

There are tanks available that mount between the frame rails behind the axle. Again, there has to be a fuel filler added somewhere, usually in the floor of the bed.

For the valving, don't run the fuel lines into the cab. You have to switch both fuel and return, and running all those lines into the cab is iffy for safety. Get the motorized Pollak valve. It mounts to existing holes in the passenger side frame rail, and it comes with the switch. The stock unit was a one-wire solenoid valve that was less reliable. I would only recommend going with the one-wire solenoid valve if you already had the other switch on the dash to run it.

The easiest solution (if you can't just mount a 20-gallon tank on a long bed) may be to put a tank in the bed, like the ones the lawn and garden people put in their trucks to fuel their equipment with. You don't need to modify your truck, and the tank itself can be moved to another truck, so it has residual value for resale or use in another truck later. https://www.google.com/?gws_rd=ssl#q=pickup+bed+fuel+tank

 

[OneShot]

Thanks, it's a long bed, so I might just swap in the 20 gallon tank. I'll go to the local yard and see if there are any I can pull that aren't rotted to pieces. I get about 13mpg so adding another 52 miles/ tank should be good for now, and I can add the driver's side tank in the future if I need it.

So if I get the 20 gallon tank, what else will I need to get? Will the filler neck, fuel line, breather, mounts, etc. all be in the same place, just a bigger tank?

And while the bed tank is a great idea, and I could fuel other stuff with it too, I have a toolbox back there because I have the standard cab and have nowhere else to put my crap, and I don't want to sacrifice that much bed space.

 

[rich weyand]

Do yourself a favor and buy a new 20-gallon tank. You may be able to find one, but even if it looks good from the outside it could be full of rust and sediment. They're $95.
http://www.classicparts.com/1973-81-Gas-Tank-Pickup-20-Gallon/productinfo/23-954/#.VCxLnVcQeRs

Also, get new fuel filler hoses, new hanger straps, and new anti-squeak stuff. Probably new fuel lines to the first hard line as well. After this many years, all that stuff will be hard to get off and will probably not go back on well. LMC has most of that, and so does Classic.

You can use the same sender unit and the same metal filler neck. Clean and inspect the sock on the end of the sender unit before you reinstall it.

 

[OneShot]

Sounds great, thanks! I'll probably rhino-line the tank too to match the underbody. Previous owner had it lined at 54000 miles and I'm at 76000 miles now. Put the new 350 in at 75000 so it'll be in pretty decent shape once I'm done with it. Thanks for the help! I'll post pictures when I'm done for others.