There's more reason now than...
There's more reason now than ever to protect your petrol.
Gas tanks have become a subject of interest recently because of how much it costs to fill our tanks. As our Corvette's go-juice becomes more precious, it's appropriate to examine the hardware that holds and protects the gasoline. The tank itself is mostly hidden from view and keeps a fairly low profile in the maintenance category. Primary reasons for replacing a Corvette gas tank are rust damage (from inside or out), collision damage, and cosmetics (as in restoration).
The appearance of rust damage on or in gas tanks is a puzzler to some people. The tank was unpainted from the factory, but the silver-colored sheen of its surface looks somewhat similar to galvanized or galvanic plating. And the surface acts like it has some form of rust-preventative coating-entire areas can be rust-free, even though adjacent areas suffer from extensive corrosion.
Extensive rust is evident...
Extensive rust is evident on the exterior surface of this New Hampshire Corvette gas tank. Tanks are unpainted and the thin, plated coating is fairly fragile. Tanks can also rust-through from the inside out when trapped moisture accelerates the corrosion.
The name of the coated steel used for gas tanks is Terne steel. This type of steel was primarily selected because of how the upper and lower halves of gas tanks are made. Each half is pressed from a flat sheet of Terne-coated steel. More specifically, each half is deep-drawn and the lubricity of the coating helps the steel slide on the tooling as the steep sides are formed. Terne steel has a dull gray finish from its coating, which consists primarily of lead with a little tin. Another attribute of this particular coating is it provides good corrosion protection when in contact with petroleum fuels.
Original Corvette tanks were made of Terne steel and had no zinc (galvanize) or nickel coatings according to Gary Whiting, president, Quanta Products LLC. The Quanta reproduction tanks are made with Ni-Terne steel, which has an additional flash coating of nickel applied to the steel before the traditional Terne steel lead-tin coating is applied on top. The underlying nickel coating provides a greater measure of corrosion protection.
We cover what's involved in removing and replacing a C2 or C3 gas tank and its related components.
For those readers who don't need to replace their tanks, there's a sidebar above on how to easily vacuum water and debris from the inside of the tank. This prevents corrosion or rust-through from the inside and helps keep down-stream parts, such as the carburetor and engine, clean and happy.
| Difficulty Index - 2 Wrenches |
| Anyone's Project: no tools required | 1 Wrench |
| Beginner: basic tools | 2 Wrenches |
| Experienced: special tools | 3 Wrenches |
| Accomplished: special tools and outside help | 4 Wrenches |
| Professionals Only: send this work out | 5 Wrenches |
| Things You'll Need |
| Gas tank | $219 |
| Anti-Squeak Strips | $5 |
| Hold Down Straps | $40 |
| Sending Unit | $70 |
| Gas Cap | $30 |
| Overflow Kit | $48 |
| Hose and clamps, tank to fuel line | $7 |
| Hose and clamps, tank to separator | $7 |
| Hose and clamps, separator to vapor line | $7 |
With the body-off, it's easy...
With the body-off, it's easy to see how the front of the tank rests on a removable crossbar support. Removing the crossbar enables the front of the tank to rotate down and allows the tank to drop out from below.
The rear framerail supports...
The rear framerail supports the rear of the tank. Although this is a custom frame featuring a late-model suspension for C2s and C3s, the tank-mounting location is the same as on an original frame.
The tank is one of Corvette's...
The tank is one of Corvette's bigger parts, but it still can be shipped to your door. Quanta includes the filler neck gasket, filler neck screws, sending unit rubber gasket, and lock ring with each new tank.
The antisqueak strips are...
The antisqueak strips are likely to need replacement, and a pair only costs $5. If your hold-down straps are rusted, a new set can be purchased for $40.
The gas tank sending unit...
The gas tank sending unit has an internal coil of resistance wire that can eventually break due to wear from the slider. consider replacing the unit even if it is not rusted. The failed sending units I've dissected usually wore out at the quarter-tank level. I'd surmise the owners didn't like to fill their tanks. And that was when a gallon of gas cost only...oh, never mind.
The sending unit is held in...
The sending unit is held in place in the tank by a lock ring; a rubber seal goes between it and the tank. The fuel strainer comes with the sending unit, but it can also be ordered separately if the sending unit is not being replaced.
Parts located on the top of...
Parts located on the top of the tank include the overflow boot, nipple, drain hose, hose spring, and tie-down straps, available together in an Overflow Kit. The purpose of these parts is to drain any gas overflow to the ground during a fill-up, to avoid the exhaust, spare tire carrier, and other parts. The remaining top end parts are the filler neck gasket, screws with o-rings, and gas cap.
After draining the gas tank,...
After draining the gas tank, remove the spare tire carrier and cover. Use caution when removing the long front bolts; you don't want to break loose their weld nuts inside the frame. A forthcoming article will detail restoration and replacement of these parts.
Slide the clamps out of the...
Slide the clamps out of the way, and then carefully break the hoses loose. If the hoses are being replaced, slit them longitudinally to ease removal. Wear safety goggles and keep your head away when removing the hoses to prevent gas getting into your eyes.
If there's a fuel-vapor separator...
If there's a fuel-vapor separator on your tank, it's located on the top left side. Although it is a challenge to see or reach, treat it gently, especially when removing the hoses. If the separator is original, the plastic will be brittle, and replacements can be hard to find.
Oil the exposed threads and...
Oil the exposed threads and remove the bolt from each hold-down strap. There's no need to worry about the tank falling; it is still supported by the crossbar. While you're there, inspect the framerails for surface rust. When the tank's out, it's an opportune time to brush on the POR-15 rust preventative paint.
Remove the four bolts that...
Remove the four bolts that attach the tank crossbar to the frame. A 9/16-inch box wrench can be slid inside the frame to hold the bolt head. Leave one bolt on each side connected by a thread, support the tank by hand (it's light when empty), and finish removing the crossbar. Lower the front side to remove the tank.
Two tabs determine the alignment...
Two tabs determine the alignment of the sender in the tank. Press the sender against the rubber gasket and engage the lock ring by hand. Then use a punch or screwdriver to slowly tap the cam lock ring around until it is fully seated.
The threaded holes for the...
The threaded holes for the filler neck screws open into the tank, so make sure the o-rings are in good shape on each screw. To the left of the filler opening is a pressure-relief valve. This particular one took a while to seat properly.
There's nothing tricky about...
There's nothing tricky about the installation; it's just the same steps in reverse order. However, before tightening the hold-down straps, check the position of the antisqueak strips between the tank and crossbar or frame, and check that the tank is centered in the frame.
Some areas of this tank are...
Some areas of this tank are completely rust-free, while other areas are heavily rusted. This is common when the plated lead barrier coating of Terne steel begins to deteriorate. The filler hole is considerably larger on this '77 tank to permit insertion of the rubber bladder.
The '75 Corvette model year...
The '75 Corvette model year introduced a gas tank with a reinforced rubber bladder to reduce the chance of gas leakage after collisions that damaged the tank. An added benefit is that as long as the bladder is in good shape, rust perforation of the tank won't cause a leak.
If your tank is original,...
If your tank is original, there may still be a buildsheet (tank sticker) glued to the top surface. That's another reason for removing the tank-to preserve the sheet, which lists the options the car was built with. Photograph the sticker before attempting to separate it from the tank. These scraps were all that was left of mine.
Tank Maintenance-Vacuum Water and Debris
Inevitably water and dirt get into a gas tank. Dirt that passes the fuel strainer can cause problems with everything downstream, from the fuel pump valves to the carburetor, and, ultimately, cause engine problems. The effect of water on these parts can be just as bad or worse. water is heavier than gas and settles into the lowest part of the reinforcing channels stamped into the tank, which can cause the tank to rust-through from the inside. Fortunately, it's fairly easy to remove any water and dirt from a gas tank of a '63 to '74 Corvette by using a length of hose and a small metal tube.
Attach about eight feet of...
Attach about eight feet of transparent 1/4-inch rubber hose to a 1/4-inch brake line that's 12 inches or longer. The clear hose makes it easy to see, and, therefore, not taste the gas when starting the siphon. The 1/4-inch diameter produces a convenient slow rate of flow.
Insert the tube into the tank...
Insert the tube into the tank and position it in the front of one of the recesses at its lowest point. A strong flashlight helps, but you can also feel when the tube slides down into the recessed areas.
Start the siphon to vacuum...
Start the siphon to vacuum the water and dirt from the tank. Tip: bump the car slightly to cause the gas to move; this helps to see the edges of the water puddles beneath the gasoline.
A few minutes of gas tank...
A few minutes of gas tank maintenance can prevent future problems by removing water and dirt visible at the bottom of the container. The siphoned gas can be salvaged by pouring as much of it as possible into a second, clean container. If no dirt or water was transferred to the second container, this gas can go back into the tank.