It could still be a head gasket or crack somewhere. I have had them where you will get the smoke until the engine warms up and the heat expands everything and it seals itself back up. I have also had one where there was a bad head gasket but if you let the vehicle sit long enough the bad spot would rust up and seal until you put some stress on it like high rpm and then it would let go again.
I can't think of any thing else that would cause your white smoke but someone else on here might have more ideas.
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1998 EB Expedition 4X4 200,000+, 1999 Windstar 200,000+ (Needs Head Gasket), 2008 Chev Colorado (Company Truck, Really sucks but it's free)
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