First,the fuel tank capacity of the W124 wagon (as well as the W210 wagon) is approximately 18.4 gal including a 2.5 gal reserve. Check the tank for damage by inspecting the tank from under the car. It is very easy to bottom out the rear of the car, compressing the floor of the tank. IIRC the fuel pickup is conveniently located where the tank gets damaged. The PO of my 300TE wagon damaged the tank in this fashion which reduced the usable capacity of the tank to 16 1/2 gallons or so. Mark