Draining Anti-Freeze

I just wonder if a quart or two is enough to crack it?  The antifreeze that was in it was good to +5 degrees.  According to our forecast for this weekend that might not be good enough.  That's why I drained it. 

Yep, always pull the petcocks and rod them out good, sedimentation not only prevents drainage, it rapidly degrades cooling system performance.

As to wether a quart or two will CRACK the block, YES... especially if that quart is intermixed with crud.  Happens ALL the time, especially with marine engines... the crud makes the water into mud, which keeps it nicely in one area as the crystalline structure builds.  Water reaches it's maximum density at about 39F, as it freezes, it becomes less dense (it's expanding, right?)... expanding to about 9% greater volume, and it can exhibit well over 100,000psi of expansive force while doing so.

An aside note, one of the biggest mistakes people make with marine engines, is proper winterizing process, which includes removing the petocks and rodding out the passages at the end of each season.  Most mechanics are lazy now, and instead of pulling the drain plugs and rodding them to drain the blocks, will just drop the drive in a garbage can of anti-freeze, which gradually becomes more and more diluted with block water and crud as they proceed through the 'fleet', the last boat being practially unprotected against freezing, and ALL blocks gradually building up the bottom half with crud, and after 6-7 seasons, blocks start cracking, and engines start overheating, requiring replacement (now out of warranty).

In all my boats, cars, trucks motorcycles, generators, forklifts... I may have flushed and scrubbed out cooling passages that would likely never have caused a problem, but I've flushed some out that were so dam-packed tight with crap, that they were NEVER gonna cool right, and once cleaned out, fitted with new frost plugs, gaskets, water pump rebuild and thermostat, ran like they were brand new.