So did the z stat start to open at the same time as the wahler or was it later than 160 in the water pot test ?

 

Surprisingly, it did, within 2 degF of each other. The Wahler opened a little earlier. I didn't make much of it before I put the original low temp tstat in, but the largest spring "rattled". When I returned it, the parts guy said "hmmmm, why is this rattling"? I said it rattled since being received. He (a little bit reluctantly and even with my data collection and "fancy" graphs) reluctantly accepted it back for a refund. 73 bucks is 73 bucks. Be wary of the "rattle", perhaps.