The fuel tank is mounted under the boot floor on all models, and both the tank design and its associated filler arrangement changed several times during production. Identifying the correct tank, sender unit, and filler components depends on the car's chassis number and production period. The MGC and MGB GT V8 share the contemporary MGB tank type in capacity and external dimensions.
Tank Designs
Two principal tank designs were used. The original tank, fitted from 1962 to early 1965, was a wedge-shaped unit with a flat top and curved bottom, made with separate end plates and held in place by two mounting straps with rear hangers secured by clevis pins. From a change point in March 1965, a larger tank of approximately 12.7 gallons (58 litres) was introduced, shaped like a basin fitted with a lid, bolted directly to the boot floor rather than strap-mounted. This second design is the same bolt-on tank used on the MGC and continued through chrome bumper production into the early rubber bumper era.
From January 1974, the drain plug in the fuel tank was discontinued. In August 1976, a redesigned tank was introduced with a combined fuel feed and gauge sender unit, a shorter vertical filler neck in place of the earlier longer sloping type, and revised pipe connections. A further change to the filler tube was made in late 1977. The tank originally fitted to 1975 to 1976 rubber bumper cars can be replaced with the earlier bolt-on type together with the corresponding filler hose and filler pipe from the pre-1976 specification, an important consideration for owners of cars from this production window.
Filler Pipes & Seals
The filler pipe and tank-to-filler hose differ between pre-1976 and post-1976 cars, as do the filler neck seals and hose clips. These components are prone to deterioration with age and should be inspected whenever work is being carried out in the boot or rear of the car, as a perished filler neck seal or cracked hose is a common cause of fuel odour in the boot area. A rubber grommet seals the filler pipe where it passes through the bodywork, and a perished grommet allows water to reach the tank mounting area, accelerating corrosion of both the tank and the surrounding boot floor.
Sender Units & Fitting
The tank sender unit changed across production. Earlier tanks used a separate sender unit secured by screws and sealed with a cork gasket, while the later redesigned tank from August 1976 used a combined sender with a rubber seal and locking ring. Sender unit kits including the seal are available for both types. Inaccurate gauge readings are usually caused by a faulty sender rather than the dashboard gauge, and the float arm can bend or the float develop a leak, giving a permanently low reading.
Tank fitting kits containing all packing strips, bolts, nuts, washers, and caged nuts are available for the bolt-on type tanks and should be ordered alongside any replacement tank, with the foam seal between tank and boot floor renewed at the same time.
Filler Caps & Tank Materials
The original non-locking fuel filler cap was a plain knurled-edge type, originally in stainless steel and later chrome-plated, used throughout production and also on the MGC and MGB GT V8. A range of alternative caps including locking, quick release, and decorative styles is available, and when fitting any alternative cap the tank venting function must be maintained, as a non-vented cap on a vented system causes fuel starvation under sustained high-speed driving. Aluminium replacement tanks are available as an alternative to the steel original, unaffected by the corrosion or ethanol attack that can affect steel tanks, fitting on the original mounting points for direct replacement. Modern E10 ethanol-blended petrol places harsher demands on fuel-system components than the leaded fuels of the era, so owners should check fuel hoses for compatibility and monitor the system for leaks.