If you've spent more than five minutes working on a Squarebody, you probably already know that your 73 87 c10 fuel tank is one of those parts that's either working fine or making your life a total nightmare. These trucks are iconic, no doubt about it, but the way GM decided to handle the fuel storage back in the day was… well, a little unconventional. If you're smelling raw gas every time you walk into the garage, or if your fuel gauge is bouncing around like it's listening to techno, it's probably time to stop ignoring that old metal box hanging off your frame rail.
The 1973 to 1987 Chevy trucks used what most people call "saddle tanks." Instead of being tucked safely between the frame rails behind the rear axle like most modern pickups, these tanks are strapped to the outside of the frame, right under the cab. It's a design that has sparked plenty of heated debates at truck shows and on internet forums for decades. Whether you're doing a full restoration or just trying to keep your daily driver on the road, understanding how these tanks work—and how to fix them—is part of the Squarebody ownership experience.
The Reality of the Saddle Tank Setup
Back when these trucks were being pumped out of the factory, the dual-tank option was a huge selling point. It meant you could haul a heavy load across state lines without having to stop every couple of hours. But as these trucks have aged, that dual-tank setup has become a source of major headaches. You've got a mechanical selector valve that likes to get stuck, two different sending units that can fail independently, and miles of rubber hose that is likely dry-rotted and cracking by now.
The biggest issue with the original 73 87 c10 fuel tank is simply age. Steel tanks don't last forever. Condensation builds up inside over the years, especially if the truck has sat for a while. That water sinks to the bottom and starts eating away at the metal from the inside out. By the time you see a damp spot on the outside of the tank, the inside is probably a rusty mess. If you're constantly clogging up your fuel filters with fine brown sediment, that's a dead giveaway that your tank is toast.
Deciding Between Repair and Replacement
I've seen guys try to "seal" an old tank with those pour-in kits. While those can work in a pinch for a rare motorcycle tank, for a C10, it's usually more trouble than it's worth. New reproduction tanks are surprisingly affordable, and they're way more reliable than a 40-year-old piece of metal with a patchy internal coating.
When you go to buy a new one, you have to be careful about the size. Depending on your wheelbase—short bed vs. long bed—you're looking at different capacities, usually 16 or 20 gallons per side. Make sure you measure your old one before hitting the "order" button, because trying to wedge a long-bed tank into a short-bed frame is a recipe for a bad Saturday afternoon.
The Case for Relocating the Tank
If you're doing a custom build or an LS swap, you've probably considered getting rid of the saddle tanks entirely. This is one of the most popular mods for these trucks. Most people choose to move the fuel storage to the rear, mounting a single larger tank between the rear frame rails.
Why do this? Well, for one, it's a lot safer if you're worried about side-impact collisions. But more practically, it cleans up the sides of the truck. If you're lowering your C10—which, let's be honest, most of us are—those saddle tanks hang down pretty low. A relocated 73 87 c10 fuel tank tucked up in the rear gives you way more ground clearance and makes it easier to run a clean dual exhaust system without having to snake pipes around the fuel boxes.
A common trick is using a fuel tank from a 1980s Chevy Blazer or Suburban. These were designed to fit between the frame rails and can hold anywhere from 25 to 31 gallons. You'll have to get creative with the filler neck—usually either cutting a hole in the bed floor or hiding it behind a flip-down license plate—but the peace of mind is usually worth the extra fab work.
Dealing with EFI and Modern Fuel Needs
If you're moving away from the old-school carburetor and jumping into the world of electronic fuel injection (EFI), your fuel tank needs change drastically. Carbs are happy with about 5 to 7 psi of pressure, which a basic mechanical pump on the side of the engine can handle all day. EFI needs way more—usually around 43 to 58 psi.
You can run an external inline pump, but they're noisy and tend to overheat because they're not submerged in fuel to stay cool. The better way to go is an in-tank pump. Many companies now make a 73 87 c10 fuel tank specifically designed for EFI. These usually come with internal baffling to keep the fuel from sloshing away from the pickup during cornering, which is crucial because even a split second of "fuel starvation" can make an EFI engine stumble or stall.
Installation Tips and Common Pitfalls
If you're sticking with the original side-mount style, installation is pretty straightforward, but it can be a literal pain in the neck if you're doing it on your back in a driveway. The straps that hold the tank in place are often rusted thin, so do yourself a favor and just buy new ones along with the tank.
Always replace the sending unit while the tank is out. It's a cheap part, and there is nothing more annoying than getting everything bolted back together only to find out your gas gauge is still stuck on "E." Also, pay attention to the "anti-squeak" strips. These are the pieces of rubber or felt that go between the tank and the frame. If you skip these, you'll hear a constant metal-on-metal rubbing sound that will drive you crazy within three blocks.
Another thing to watch out for is the ground wire. These trucks are notorious for bad grounds. If your fuel gauge is acting wonky, it's almost always a bad ground at the tank or a pinched wire along the frame rail. Before you bolt the tank up tight, hook up the wires and have someone watch the gauge while you move the float arm by hand. It's a five-minute test that can save you two hours of taking it all back apart.
Keeping the Fuel Lines Fresh
While you're messing with the 73 87 c10 fuel tank, don't forget about the lines. If you're still running the original nylon or rubber lines from the Carter administration, they're probably about as flexible as a dry twig. Today's fuels have a lot of ethanol in them, which eats through old-school rubber like acid.
Make sure you're using SAE 30R9 rated hose if you're replacing sections of rubber, as that stuff is designed to handle modern fuel blends. If you're doing a full overhaul, running new NiCop (nickel-copper) or stainless lines is the way to go. It's a bit of work to bend them, but you'll never have to worry about them rusting out or leaking in your lifetime.
Wrapping It Up
At the end of the day, your 73 87 c10 fuel tank is the heart of your truck's "food" supply. Whether you keep the original saddle tanks for that vintage feel or swap in a rear-mounted aluminum cell for a modern Pro-Touring build, getting it right is the difference between a reliable cruiser and a truck that leaves you stranded on the side of the highway. Take the time to do it right, check your grounds, and maybe—just maybe—you'll finally be able to stop carrying that "emergency" five-gallon gas can in the bed.