go back to the parts store and tell the guy to look up a gasket for the thermostat housing

this is a generic diagram, but item #2 is the gasket. also be sure the surfaces are still clean ( they look good in your pic) apply a thin even coat of copper gasket compound to both sides of it (below)

http://www.justanswer.com/uploads/Mo...340_tstsat.gifhttp://www.shopthedude.com/filedb/6/0/19506.png

Makes no sense it seals with one housing and not the other.

Are you sure you didn't crack the new one when installing?
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Be sure to check the fetzer valve.

No, the new thermostat housing is in installed in my car. It leak with it on, so took it off and just installed the the body. No leaks. My old one is in the trash.

dude, it has to have a gasket.

Then the thermostat must not have been in the groove all the way
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There was no gasket when I took it off, just an o-ring.

okay so no gasket needed, but this video shows the oring gets a gasket sealer applied to it

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Flip her over Henry.

o rings are supposed to be installed with no sealer. In fact I use very little silicone.
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agreed, but I normally see oring seals in oil related apps, like distributor housings etc. couldn't hurt to put the sealant on there, follow the directions and it should hold.

I just don't know why it would leak from the housing with the new thermostat and then not leak with the thermostat out. It's spewing out and both nuts were tight.

there is a lil guide ridge in the housing -- without the thermostat in there, that ridge does not bottom out inside as you crank it tight. with the thermostat in, now it bottoms out inside and you can't completely cinch it down.

BTW- where you are, the climate is mild during winter -- you don't need a thermostat, really.