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It sounds like you have a bad head gasket or a cracked head . This can be confirmed with a combustion gas test of the cooling system.
The symtoms of a bad head gasket or cracked head are:(can be all or just a few of these)
A miss on cold start up
White smoke out the exaust (steam)
Unexplained coolant lose.
Wild temp changes up and down.
You can try plulling the plugs out and pressure test the engine overnight and in the morning cranck the engine over without the plugs in while watching to see if any antifreeze comes shooting out of the spark plug holes If it does you have to tear the heads of have them pressure tested and replace the head gaskets or gasket.