Interesting the fuel lubrication/cooling theory. I worry about this too, however, curiosity gets the best of me! On my Prius I have run the tank dry about 4 times with 2 gallons to refuel. No problems with the fuel pump, and figured out the car had about 2.3 gallons remaining (120mi) after the range went to "0" and the Fuel gauge flashed empty, nice to know! Now I have the Energi :-) With a full battery (approx. 20 mile range worst case) I go to "EV only mode" when the range = "0". When the ICE finally dries the tank I have had between .46 and .51 gal of fuel past the "0" range mark. Ford plans on this happening. At the moment the fuel is completely exhausted, 1. The A/C compressor shuts off. 2. The map shows all the gas stations. So, they 'plan' on people to run out of gas, on purpose, or by mistake, and do everything they can to help get you to the station. Clearly the fuel pump shuts off after the last drop gets pumped, so I am not so concerned about the fuel pump burning up...
