Peter: The problem isn't the water in the gas (at these temps), it's ice blocking the lines! I used to use drygas in my tractor - it works when you add it to the tank before the water freezes. Once it becomes solid, you have to wait for the thaw to start it! (I used to take the line off and blow it out, but that's not so easy on a car...)

I need to do a citric flush myself, I'm afraid. I had very poor heat and my idea of vinegar and baking soda run through (JUST THE) heater core helped, but not enough to please me. Once I patch my rad up again (It was leaking heavily, I soldered it, it began leaking in another spot, I soldered that, now it's leaking in 3 spots that I need to solder - all different than spots I've previously fixed!)