I think I may have a faulty thermostat. Anyways to check it without draining all the coolant?

 

Warm the rig up from cold with the radiator cap off. When the thermostat opens, you will see strong circulation that is obvious in the filler neck.

It's not foolproof and it can make a mess if the fluid is full and comes up the neck, but barring taking the thermostat out and thus draining the fluid, you don't have many other options.