BMW has always recommended their own fairly expensive coolant. This can make life difficult on a Saturday afternoon if you have not planned ahead. Rumors on the web peg the blue factory stuff as everything from off the shelf Peak to various flavors of european unobtanium. What I do know is the the blue factory stuff is possibly the best thing out there for the delicate factory aluminum radiators with plastic tanks. I have run a number of my BMWs well above 200k miles using the factory blue stuff. After doing some research, I think I may have found what the coolant is. Pentosin makes a NAP free (Nitrite, Amine, Phosphate) coolant, part # G001100, that appears to be the same shade of blue as the factory coolant. It may or may not be cheaper than factory stuff depending on what sort of a discount your parts guy gives you at the stealer. It appears that the Pentosin 1.5 L bottles go for $7 to $8ish. Please note that this NOT the "lifetime" long life stuff nor is it non-toxic. You better change your coolant every 2 years and don't let the dog near the drain pan. If your car has pink coolant or requires long life stuff, look elsewhere, possibly the pink Pentosin G001200.