ATF should not freeze I would think... not at -20 anyhow... maybe you got some water from condensation in there or something? That said, I don't see a problem with synthetics in the carbs. As long as theres something in there thats comparable in viscosity to regular atf.

When its that cold, your block heater is a God sent... especially if its a good one that replaces one of the knockout freeze plugs in teh water jacket. The other biggie thing that will really help in them cooooold temps is to tote your battery inside at night. Seems like a PIA, but its a lot easier than fussing with jump starts, battery chargers, etc...

Unfortunately, I had my shoes off last night before I thought of that... so I might be in trouble today. We'll see. We only hit abotu -10.

-Matt