All cements based fillers shrink I've used Moroso block filler once and it shrank away from one freeze plug after it pushed it out enough to need replacing I've heard that "Hard Block" brand filler is a epoxy filler and doesn't need to cure 30 days and it doesn't shrink also I also heard it does expand and shrink I haven't used it so I don't know about it either way
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)