so not normal. even after a top end job you may have to change the oil once after a short run but that should be it. either the head gasket is suspect or the intake is leaking, very easy for the intake to leak. a compression/leak down will give you some info but you are looking at a tear down. I always put a very thin coat of gasket sealer around the coolant ports to aid in sealing, nothing thick but this is a common thing to happen. also did you use a nice thick 1/4" bead of gasket sealer on the ends of the block or the cork/rubber gasket peices ?