Soldering iron calibration/bad heater?

[XOIIO]

Hey all, since I got a multimeter with a thermocouple I decided to check my soldering iron's true temp, I've used it at 450 C ever since I got it since it was second hand, turns out that was only around 230 C, talk about out of calibration! I'm working on calibrating it now, but it's proving finicky, I got it to stay at around 300, but when I turned it up the temp went down, so I'm still figuring it out. Is the heater perhaps dyeing out? There isn't much range on the trim pot. This is a hakko 936 by the way.

edit: thermocouple slipped off the iron, no wonder the temp went down a bit 

edit2: whoops, didn't delete the whole old title.

[dexters_lab]

maybe the same 'issue' i had with my Xytronic?

https://www.eevblog.com/forum/reviews/xytronic-lf-1000-soldering-station-calibration/

Mine wasn't that far out though

The size of the tip and the point your measuring affect it greatly, in a long and fine tip i would expect the error to be greater than a stumpy thick chisel tip for example

[staxquad]

Hey all, since I got a multimeter with a thermocouple I decided to check my soldering iron's true temp, I've used it at 450 C ever since I got it since it was second hand, turns out that was only around 230 C, talk about out of calibration! I'm working on calibrating it now, but it's proving finicky, I got it to stay at around 300, but when I turned it up the temp went down, so I'm still figuring it out. Is the heater perhaps dyeing out? There isn't much range on the trim pot. This is a hakko 936 by the way.

edit: thermocouple slipped off the iron, no wonder the temp went down a bit 

Authentic 63/37 is a eutectic alloy, which melts at exactly 183 °C  or 361.4 °F.