The simplest way to check this would be feel.  Feel the hose coming from the
thermostat.  Feel the other hose.  The hoses will get warm and then hot while
the one from the Thermostat will stay cool.  Then when the engine reaches
temp and the thermostat opens, this hose will get warm and then hot.
Also you could put your hand on the radiator and see if it is getting warm.
Usually they get warm at the bottom but stay cool at the top until the
thermostat opens.

Keep it simple.

Ken Wilford
http://www.vanagain.com
John 3:16
Phone: (856)-765-1583
Shop:   (856)-327-0027
Fax:     (856)-327-2242