Steve and all,
I used to work on ovens and occasionally had to check the thermostats. The very nature of thermostats means that they will always go over the selected temperature before turning off, and drop below the selected temperature before turning back on. We always waited a couple of on/off cycles to allow things to stabilize, then average the temperature and compare that to what was set on the thermostat.
So my steps were:
1) Turn on the oven, set the thermostat to 350 degrees.
2) Wait until the thermostat turned off, then on, then back off.
3) Wait for the temperature to peak, then record that temperature.
4) Watch the thermometer and record the lowest temperature when it will turn back on.
5) Go through this cycle at least 2 times, usually 3...
The result would be something like this:
High Temp Low Temp Average
375 330 352.5
370 330 350
370 330 350
Most of the time there would be about 20 degrees over/under the setting, but the average would come out 350.
Occasionally, I would see a thermostat that only had a 10 degree over/under setting but it was usually more.
On these ranges there was an adjustment on the back of the temperature selection knob and say the average was 330 when you had it set for 350. You simply removed the knob and made an adjustment.
Steve, your 100 degree difference does sound like a bad thermostat.
Keith
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