The GM dexcool coolant is the orange stuff. It's total junk (eats up intake gaskets in GM vehicles)... The claim is that it is to offer a longer life coolant. It **WILL NOT MIX** with other coolants. It turns in to some orangery booger goo. Since you have not started the vehicle it has not made it fully in to the system. Water jackets, heater core etc..

On left side of the radiator (vehicle left, your right from the front) down toward the bottom will be a drain plug. You need to open this and collect what comes out. You will then need to fill it up with water and drain it again a couple of times.

Fill it up with water again and drive it with the heater on till it gets up to operating temp and heat is coming out. Let it cool off and then open the drain plug again.

At this time fill it up with the good stuff 50 coolant/50 distilled water. Two of the BMW gallon jugs will be MORE than enough.

Don't forget** Don't do this hot. You will get burned. Also, when opening the cooling system always open the bleeder valve on the expansion tank when filling.

You made a mistake but you have not caused any damage. Just get that junk out of there.

Brandon