There's probably a good bit of coolant in the block still. My Jeep holds about 3 gallons, excluding the overflow bottle. Even after draining the rad, pulling a heater hose and holding it up (which let out about another 1/2 quart from the block/core), and pulling the water pump, I never got more than 2 gallons out of it. And having the water pump out means that the upper part of the block, heads and intake manifold were dry, leaving a gallon or so between anything left in the heater core, and the lower areas of the block.