Yesterday I drained my radiator to change out the upper and lower radiator hoses and to be sure I had the true blue BMW coolant in the system. I flushed the system by disconnecting the upper radiator hose at the radiator, and then running a garden hose into the expansion tank at relatively low flow rate. Started the car and let it run for 20 minutes. During this time the fluid coming out of the upper hose slowly changed from a mixture color (greenish) to clear. After five minutes of clear I felt pretty good the system had been flushed. By the way, the heat was running full hot and full blower during this time to insure all lines were being flushed.

I then changed hoses, and refilled the system with pure coolant, as I did not drain the engine block during this process. After a few cycles of running, bleeding, cool down, refilling, I had put a total of 5.5 quarts of coolant and 1.5 quarts of distilled water. The system was bled, temp was rock steady, and no leaks.

First the tip: After all of this the low level coolant warning remained displayed on the dash. I checked the connection below the expansion tank, no luck. I then took a long screwdrive and inserted it into the expansion tank, tapped the sensor a few time and this took care of the warning. Seems it got stuck closed when the system was drained down.

Now the question: By my math I have about 4 quarts of regular water in my cooling system. How big of a deal is this if I plan on flushing my system every other year?