Max J. Sandler,
It is hard to say, really, what the problem might be, but I have found some filling stations with relatively high pressure hoses and they can cause the filling procedure to become a challenge. The agitated gas foams a little (nothing compared to Diesel!) and trips the shut off sensor. It also seems to pressurize the air in the tank, and you get air pushing back out as the gas is going in which also makes the little trip device shut off. Have you tried putting the filling nozzle on the lowest flow rate notch and seen how much gas you get to go in?
Seems to me if you are getting expected engine performance (starting, throttle response, mileage) on the 13 gallon load you put in, there is really nothing much else wrong. And exhaust gas temps are higher on cars with active catalytic converters, so melting a plastic bag after it is warmed up is not really alarming.
Hope this helps, Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)