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possibly t stat but where did all the coolant go?? if its not leaking, its being burned in the engine...

 
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You might have a clog or a bent hose somewhere preventing the fluid to circulate

That's the best answer I can come up with

If it were me, I would try to completely drain the coolant from both drains, drain the reserve tank, and completely refill all coolant, then see if the problem persists

And please dont start a pissing contest between other members, I saw your other post, and would appreciate it if you dont give an attitude when someone gives a reply
We try the best we can to get to all the posts, but sometimes might miss one or two.
and it bothers us more when people bring up 5+ year threads to start a something when we could be answering questions like yours