Originally Posted by civicized

While you've got your thermostat out, throw it on the stove in a pot of water. It should open all the way before the water boils. If it's good, and if your hoses are hot on both top and bottom when you run the car without the thermostat, then you have to ask yourself why it isn't opening when in the car.
Only two reason - mad amount of air in the system (not too likely) or as stated before, your bypass hose is plugged up or not hooked up right.