rickjordan,

The fuel is stored at the filling station at some prescribed distance below the surface, where the temperature is a pretty constant value. When you buy fuel, and it is foaming as it comes out of the nozzle, it is at this storage temperature. Your car and tank, and within a few hours, the fuel you bought, will be at ambient temperature. In the summer this is likely to be quite a bit higher than the underground storage tank temperature at the filling station. That is how it is heated.

I believe that foaming feature of Diesel is the reason you have the "compensating tank" as it is called in my manual. I believe Diesel foams while you drive, as well as when you fill the tank. On the W115 and W123 series vehicles, there was an atmospheric vent on the fuel tank that used the compensating tank to avoid getting the foam dribbling out of the right rear corner of the car. On most models this vent is just under the right rear bumper corner. The vent is needed to prevent sucking a vacuum in the fuel tank as you use the fuel.

I doubt this feature continued as even Diesel fuel vapors are likely to be restricted by the EPA. I hope this helps. Jim

__________________
Own:
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

Owned:
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)