My son's 03 cracked the head and never missed a lick, started filling crank case with water, peged out the temp gauge and that's all she wrote. This was at hwy speed, wonder why it still ran ok?

Ummm... I'm always pre-load the system with the heater hose off till the coolant comes out... Then hook up the hose...

Depending on the location of the crack it would be very possible to not interfere with the cylinders and still act normal until it's too hot!!

yes if the head cracks between a coolant and a return oil passage the colant will leak in to the oil but the compression will not be affected as the cylenders are still sealed and no signs will show while driving till the colant level get low enough to start over heating hopefully he didnt get it too hot or hurt internal bearing do to the colant dilutin the oil

Another "war story"... my marina customer had a "raw water cooled" (ocean water) inboard "Mercruiser" Ford based V8. Came in from 20 miles off shore on the sad end of a tow rope. There were pipe plugs in the head into the water jacket with a recessed square socket under the valve covers. One of them was eroded away so a pin hole devoluped spraying water into the oil which drained into the crankcase. The rubber impeller sea water pump, pumped water into the engine as it was running. I don't know how they kept it running so long but eventually the oilly froth was ingested by the Crank Case Ventilation which shut it down! I dropped the oil pan over a huge catch basin... the crank case was filled with a cottage cheese like mess. The customer wisely junked the motor (probably a 351cid, 233 hp), I repowered it with a Chrysler Marine 440cid, rated at 330hp. My suggestion was to run at the same hull speed as before but at 3/4 throttle. I was told the owner prefered to run with only the prop in the water! (It would make that Blackfin 24 fly!)