You just need to figure out what concentration of coolant you have now:

The total volume in the system is 3 gallons (per your notes), so figure out how much straight coolant you just added (let's ASSUME 1/2 gallon).

So you must have had 2.5 gallons left in the system, and you added 0.5 gallons. The old stuff was 50% coolant, or 1.25 gallons. You added 0.5, so you now have 1.75 gallons of pure coolant and 1.25 gallons of water. That makes 58% coolant. Just run the engine and bleed the air. If you have significant air bubbles, you should add up to 1/2 gallon of water. After that, top off w/ a 50:50 mix of coolant/water.

You can do it, you can do it......

Thanks to everyone that's been helping me so far with this radiator situation. Unfortunately, I'm ready to abort the "mission". Got the new hose, got the right antifreeze, found the bleeder screw, purchased the proper tools, dressed up in my weekend "dirty" clothes, but now I think I'm in over my head. Here's the current state of affairs:
When the radiator hose blew, I think/thought all the antifreeze leaked out of the cooling system. So I purchased 2 gallons from the dealer. The parts guy said I would need 1.5 gallons of anitifreeze to mix with the 1.5 gallons of water that I would also add if the system was bone dry (which I figured it was). So...I attached the new hose and filled the reservoir with the new coolant. I then loosened the bleeder screw and coolant is coming out but there is no air coming out. What I'm thinking is that the system was not empty to begin with and now I have added over half a gallon of antifreeze (straight) to the system and now the concentration is nowhere near the 50% point. Now I can't determine what concentration of coolant I have and how to get it to the proper dilution. I'm sure there is air in the system but only coolant is coming out (alot of coolant!). Do I just let it run out and maybe there will be some air at some point? Or does this mean that the system is full? Do I start my car and see what the temp gauge does? Do I abort till monday and get my car to the shop? Damn! Damn! I was really hoping to do this solo. Is there still hope?

Patrick
88 535i