coolant loss,overheats on 2000 BMW 323i

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
started with plastic pipe under manifold busted.overheated.replaced pipes,heater hoses,thermostat,radiator,top hose,bottom hose,expansion tank,water pump,thermostat on expansion tank,flushed system,new bmw blue antifreeze.had block test for combustion gas-was neg.,took to bmw dealership and was told head gasket.OK here is mystery- no oil in anitfreeze,no antifreeze in oil,no smoke at all,runs perfect,heat gauge stays at perfect 12 o'clock until it looses water.another mystery- ran perfect last night,coolant level light did not come on and had water in expansion tank but soon as i took cap off today and vented at bleeder port water went down.apparently block was dry.i am not crazy yet but headed there.can it have a blown head gasket and still run as great as it does?? any info will be greatly appreciated.
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