Block cracks from freezing are usually to the outside, and result in coolant leaks, not compression in the radiator. Pull the head and look for warps or cracks, or a simple blown gasket. A quick check for warp across the top of the block can be done with a big, flat file. Draw-file the top of the block with a firm down pressure and long strokes. A uniform scratch pattern indicates it's flat enough to seal a head gasket. Ditto for the sealing surface of the head.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!