The 'stat should be opening at102 deg.
Try putting it in the oven at 120 (just out of curiosity!!)
When you say the new one is the same, do you mean you tested it in boiling water and it did not open, or you fitted it in the car and you are still having running problems (overheating, I assume)?
If the latter, please post the actual symptoms.
trey
April 2009