PI zero running hot

[#1]

Just put pi-hole on my original zero with heatsink (the free one from the pi mag), and noticed it is running @67C

I had it running on a pi zero w (no heatsink) and it was running @38C, but want the zero W for an other project.

Same sd-card only difference is the zero has a wifi dongle plugged in. Both headless running Jessy (no GUI or hdmi plugged in)

Anybody got any ideas why it is so hot? (top doesn't show any load, 1% running top max, 2 % running htop)

Stats from pi-hole web server

 Active Temp: 63.8 °C 
 Load:  0.06  0.06  0.01 
 Memory usage:  11.1 %

[#2]

dunno.. but on the pi zero W i got, mine was running at about 40 degrees.
that was with HDMI, and usb ethernet connected, running raspbian stretch lite.

not sure why the original zero would run hotter though.