Temperature

I think it has a temp sensor in the F5 but I'm guessing body temperature means it reads higher than ambient. Maybe you could take it off your wrist and leave it to settle and see if it then matches the temperature?

CW

Internal chip which is sensitive to the watch being warmed up by your wrist, and is mainly there to help with barometer calibration.
If you want accurate temperatures, buy a Tempe sensor.

Internal sensor. The PDF form of the manual says "To get the most accurate temperature reading, you should remove the watch from your wrist and wait 20 to 30 minutes."
Obviously an internal temperature sensor in the watch is going to be impacted by body temperature, and as you noted not much use if you want to log temperature during your run.

There's an internal temperature sensor in the va-hr as well as the f5/f5s. It's used in conjunction with the air pressure in calculations. On the va-hr , you can display it in a data field, as well as in some widgets, apps, and watchfaces, but isn't in the .fit for an activity. Same on the f5/f5s, but there it is stored in the .fit.

The sensor is in the watch itself, and is therefore impacted by things like your skin temperature, if you are wearing sleeves or jacket etc. and really isn't ambient Temperature. It's not uncommon that it's off by 10F. (a Tempe will be more accurate in most cases.).

Anyway, on the f5/f5s you can see it on a native widget too, and maybe have it as a field on a native watchface. there are also CIQ watchfaces that display it (see "Simple TEP" in the link in my sig (Temperature, elevation, and pressure).

BTW, when I got the va-hr, the first sensor I paired to it was a Tempe, and same with the f5. If you do hiking, etc, and want better temperature data, it's really the way to go. The Tempe looks just like the normal Garmin Footpod, and has the same kind of clip to attach to your shoe, but I ended up adding a carabiner ($2 US) and now can clip it to my belt, pack, even coat zipper to get a better read of the ambient temperature. On the facebook page in my sig, I have pictures, and details on the caribiner I used....

I'm disappointed to see the F5 still uses the same poor logic when being used with a Tempe, whereby if it's connected to a Tempe but misses a single reading from the Tempe, it uses a reading from the F5 instead. This results in lots of spikes during an activity where the ambient temperature may be 10 C but the trace will show lots of spikes to 20 C where it's "missed" a transmission from the Tempe and used a (body temperature-affected) reading from the F5's sensor instead.

It would be much better if the F5 simply used the last reported temperature transmitted by the Tempe if it lost contact (the temperature is unlikely to have changed much!), only dropping back to the F5's internal sensor if it received no signal from the Tempe for an extended time, say 5 minutes.