Air in system. Crack happened from an air pocket that was right there. Gurgling noise was air popping. Had an idiot put an engine in daughter's car and it was Summer time so she used AC. When she hit town she called me cause gauge was going up and down. I had her park it until I got there. No coolant in reservoir so I opened top hose filled it up then reservoir as it had a sealed radiator (GM). It took me .5 hour in a parking lot with a flashlight, 3 grandchildren and a gallon of premix. The shop tried to say we lied and even refused to pay for coolant. Lucky she listened to me that one time and didn't destroy that motor. I would get a lawyer involved as they should take responsibility which they should have insurance.