Yes, a Mercedes 300D has a fuel tank.
Between the upright of the back seat and the forward wall of the trunk
In the 1984 300 TD, the capacity is 18.5 gallons of which 2.5 gallons are reserve. It should be the same for the '85.
The fuel tank capacity of an Mercedes 300TDT is According to the Mercedes Repair manual it is 18.5 gallons with the reserve light coming on at 2.9 gallons.
its located inside the fuel tank
The fuel capacity of 1996 Mercedes e320 is 80 litres.
Via sledgehammer
When owning a car it is important to know the size of the fuel tank. For a 1983 Mercedes 300TD Wagon, the gas tank size is 18.49 gallons.
about 45 liters
Inside tank
The fuel pump is in the fuel tank and the fuel tank will have to be removed to access it. If you do not have the skill or equipment to do this properly, I suggest taking it to a shop.
Mine went out and was replaced once. Mercedes told me it is inside the fuel tank. The fuel is designed to keep it cool, so never let the fuel level fall below 1/4 tank.
Mercedes fuel tanks are behind the back seat.