Dead weight in an engine is the enemy of efficiency.       That's why airplane engines are made of aluminum.  Why Volkswagen's engine is ingeniously cast of aluminum and magnesium alloys (even lighter than aluminum).       Volkswagen reduces dead weight in still other ways.  The engine is air-cooled - no bulky radiator.  (No water to freeze in winter, or boil over in summer.)  And placing the engine in the back gets rid of the conventional heavy drive -shaft while giving direct power to the wheels.  (In mud, sand, ice, snow, where other cars skid, you go.)       As a result, the Volkswagen engine weighs only 198 lbs.. and every pound works.  You get an honest 32 miles to the gallon (regular gas, regular driving) and will probably never need oil between changes.  And the engine is so efficient, top and cruising speeds are the same.  You can go 70 mph without strain, all day long.       These are some of the reasons a used VW is worth almost as much as a new one.  Your VW dealer will show you the others.