Hose routing? I know the vx has that funky routing; the lower outlet on the radiator feeds the thermostat housing and the upper outlet feeds the front of the block, etc.
Otherwise, make sure it's the right tstat, etc. It could be a failed tstat from the factory, although that would be rare. Did you use a gasket around the new tstat?
hmm well as you know most tstats nowadays are made in india, thier quality control is crappy. to test to see if its functionign correctly take it outa the car and dangle it touching a pot of water on the stove. turn on said stove with a termometer in it and see when it pops open. my guess it aint gonna be 180 as my expereince 1/2 are bad from the start