I bought my FP2 last year and I like it.
The concept is great and our smartphones have to last longer than the other.
I will be happy to get a proof of it. I´m really impatient.
The only problem with this model is the long lasting battery and the heat of the case when I use the GPS for a drive longer as 1,5 hour.
Yeah, heat removal of the FP2 components really is a mess. Maybe you can place the phone in front of the aircondition outlets of your car. (Not sufficient when you drive your car in wintertime, I suppose…)
That one sounds very familiar. Had many reboots caused by this mid-journey. Things that help:
I am not sure, how good that works, but maybe it could help as well, to place a copper-plate behind the phone, as copper is a very good heat conductor; plastics is not.
In addition with some ventilation, this might help dissipating the heat.
Especially bad might be a holder with a plastic cradle, that is covering the phone, thus insulating it and accumulating heat.
Please keep in mind, I am no physicist and it’s just kind of guessing. (Though coolers in computers are made of metal and cooling fins are used to enlarge the surface if I got it right.)
A copper plate of 2 mm sized 70x135 mm e.g. is 8.18 € from this German shop:
https://www.prokilo.de/kupferblech-of-cu/
And here’s an offer from “banggood com (China)” 100mm * 150mm * 0.8/1.0/1.5/2/3/4/5mm Pure Copper Sheet Cu Metal Safe Using Guillotine Cut Sheet Plate - 5mm
Maybe the copper plate makes the phone suffering from heat even worse, especially in these hot summer days. (Remember the old copper pots made for cooking?)
I am joining you!
Yes, because copper is not storing the heat, but transferring it to the stuff inside the pot immediately.
I do remember that much. 
(hopefully correct)
But you are right of course. If the heat in the car is really getting up, it might work the other way around; especially when the phone is not yet hot. 
You´re right 
the winter are cold and long.
I agree with you. Maybe should I install the cooper behind the plastic or should I have to make a hole in the plastic and glue the the cooper in the plastic hole ?
I don´t know if I´m “understandable”, clear, my englisch is a bit poor.
You do not know which part(s) lie(s) under the plastic surface, I highly discourage everyone from drilling a phone! The possibility of appearance of cracks due to instabilities caused by the hole in the core unit might damage your FP2 in the long run.
I agree with @DeepSea
Though you could drill a hole in the cover, when you have taken it off.
Through a hole in the cover of the phone lots of dust, dirt and debris will find it’s way inside and most likely cause more damage than you can gain heatwise.
Even more important - all just from my personal unprofessional reasoning - there are 2 big points against that solution:
Or do you mean to replace parts of the plastic cover by copper.
If you are a real craftsman, have the neccessary tool and know what you do; go ahead. You sure will get a very unique phone and a show-stopper as well.
Please post some pictures on this thread, if you have done so; I will be curious as hell. (Honestly!)
My - less sophisticated - solution would be to put a copper plate/sheet in the cradle where you place the phone and maybe the plate/sheet can be a bit larger, so it is sticking out of the cradle. How to do it and if it is possible at all, depends on the kind of phone holder you have.
I extracted a couple of posts from the FP2 Android 9 topic to this new topic as it seemed to me that those were quite clearly focused on something largey unrelated to the original topic. Interesting discussion, btw. 
For my part, I often remove the back cover for some specific actions (mostly updates, making & restoring TWRP backups) that I already know will heat up the device; but of course that’s only viable when you can keep the phone in a stable position (either by holding the phone and pushing against the battery or by just placing the phone flat face down on a desk) for the whole time of those actions.
Your less sophisticated solution is the most clever one, but too easy (I´m unconscious enough to like some challenge).
You wrote that you aren´t a professional but, do not worry, your mind and your brain are working very well (not like mine with my silly complications 
).
Thank you DeepSea for your advices.
I thought:
1/ replacing a parts of the plastic cover with a cooper plate,
2/ drilling the platic cover (once removed) and glueing a circular piece/plate of cooper,
but, after reading closely your post, I would say that it is highly uneasy to do because of the rectangular rubber rim and two plastic pins which are pressing and the battery either the SIM-card.
I´m not a craftman only a human looking for solutions to unreleavant problems
I agree with you.
It should be done with a consciousfull mind. So better not to do it…
If the sheet sticks out, make sure it doesn’t catch sunlight. The sun will heat your whole phone instead of just the top if that is the case.
The best would be though, to have the metal in contact with air (like a heatsink) at some place. Otherwise you’ll just heat the cradle by efficiently conducting heat towards it.
Quite correct.
That’s why I had the idea to make the copper sheet larger, so it can transport the heat away from the cradle. But the sunlight heating up the metal really might be a problem. Good point!
The phone definitely should not be placed behind the windscreen (anyway) but in front of a ventilation outlet. Even if the air coming out of this outlet is warm, it will still be cooler than an overheating phone and the constant airflow will help cooling down the copper plate and phone. Like a fan in a computer.
Maybe a holder like this one, that is not enclosing the phone and making heat dissipation possible would be a good idea?
What do you think??
From amazon:
The top end should ideally not be exposed to the sun, as @AlbertJP rightfully mentioned.
Well, exposing plastic to the sun is less bad than exposing metal to the sun. I think it would work well this way. I’ve had my FP2 mounted in front of the vent before (in summer so probably with AC on) and that worked well.
I can confirm that, however my phone has also survived in a holder at the wind screen because even though I have a holder with various mounting options not everything works in every car (don’t have an own one).
About the metal heat sink ideas: Keep in mind that such measures can also affect all kind of reception of the phone. If e.g. the GPS is disturbed this may not be exactly helpful while using the phone as navigation device (especially because the phone doesn’t use Glonass etc. since Android 7 anymore, only GPS).
Good point.
Could copper even enhance reception?
In olden days simple radio antennas were nothing but a copper coax with a banana plug. 
Otherwise maybe aluminium could be used, as it is a good heat conductor as well but maybe less problematic with reception. (Btw., I just looked it up and silver and gold are good heat dissipants as well. )