There are three nozzle sizes actively in use Today:
(1) Small nozzle for Unleaded gasoline (13/16" I think)
(2) Medium nozzle for Diesel fuel (15/16" I think)
(3) Large nozzle for high-speed filling of large diesel tanks, e.g., Semis (1 1/4" I think, but I'm not sure on this size)
BMW diesels in the U.S. have a mechanism such that only nozzle 2 will go into the opening.
Unfortunately, I have found that some fuel stations do not follow the established protocol and use nozzle 1 for both unleaded gasoline and diesel fuel.
It appears you have the bad luck of living in an area where the stations are somewhat irresponsible and are using the incorrect nozzles on the diesel fuel pumps. I suspect their logic is that the small nozzle will always fit into a bigger hole, so they simply use the unleaded gasoline nozzle on their Diesel pumps. I believe this is either due to their laziness (one less nozzle size to inventory and deal with), or perhaps is due to some older diesel vehicles that may not use the larger diameter "diesel" fuel tank filler (I seem to see this mostly in agricultural/rural areas when I travel). This does a disservice to the owners of gasoline-fueled vehicles, as it facilitates them making a mistake and putting diesel into their gasoline-fueled vehicle. And they obviously did not count on the cleverness of BMW engineers, who came-up with a mechanism which prevents a too-small nozzle from being inserted into diesel-powered BMW vehicles.
I have noticed that this seems to not be station brand correlated, but more geographically correlated -- I suspect it is the fault of whatever local company services and repairs the fuel pumps for the stations in any given area.
You can explain the issue to the station owner, pointing-out that as more diesel-powered vehicles have misfueling interlocks he will lose business (which might work, but I wouldn't count on it), or keep searching for a station that has the correct nozzles installed.
Unfortunately, while I believe there is a federal law which requires unleaded fuel to have nozzle 1 installed (an emissions-related hang-over from the switch to unleaded, to ensure people did not put leaded-fuel into cat converter vehicles), I do not believe there is any legal requirement to have the proper nozzles installed on diesel pumps -- it is just an accepted convention in the industry, not a legal requirement. But laws vary by state, and perhaps a complaint to the State would result in the station correcting use of the wrong nozzle for diesel.
Hope that helps clarify the situation.
P.S. Sometimes the tip of the correct-sized diesel nozzle is bent in places, such that the interlock will not let the correct-sized nozzle in, and twisting it a little bit while inserting it gets the interlock to open-up.
Last edited by Penguin; 04-16-2012 at 10:28 AM.