you could have air pockets in the block however a fresh engine will run extremely hot when first fired / i drill a 1/8 inch hole in the outer area of the thermostats on my engines before firing them for the first time it does not affect the thermostat from proper operation but lets the water fill the block / i also run the engine with a garden hose in the filler neck of the radiator with the drain valve open while the cam breaks in / let the engine cool then fill with coolant and you should be fine!
