I got the high temp warning (I have it set to 59C).

First things first... I really think that 59C is too high a setting. Something in the 50-55 range might be better, but of course that would make the alarm come on all that much sooner.

Here's what's happening to you. Your empeg is sitting in a cavity in the dash that may well be open to the rest of the world, but there is no real air circulation going on. So the heater ducts are radiating heat into that cavity, along with the lesser amount of heat produced by the empeg itself. The longer you run the heater, the hotter that cavity gets.

Now for the real irony: putting the cooling fan in your empeg only made matters worse, because the air temperature inside that cavity is warmer than the air inside the empeg. You're using your cooling fan to blow hot air through the empeg!

Another irony is that the colder the weather, the more your empeg is going to overheat, because your heating system compensates for the cold weather by raising the temperature of the air it is using to heat the car, and the cavity in your dash gets hotter the colder it is outside.

How do I know all this? Because I have exactly the same problem with my system. I am OK as long as the outside temperature is above zero degrees F. Below that, it becomes a balancing act to keep my empeg below 54 degrees C. I have found that by increasing the heater fan speed and decreasing the heater temperature setting to 65 degrees F (I am assuming your BMW has some sort of electronic HVAC system where you can set the desired temperature) I can keep my empeg running down to about 25 below zero. Beyond that, I have to pull the empeg out and let it cool down after an hour or less of play.

The best solution (one I haven't tried but maybe will some day) would be to install a small, quiet, low volume fan to circulate air through the dash itself -- exchange the quite hot air in that dash cavity where the empeg is sharing space with your heating ducts with the cooler cabin air. Wire it so that any time the heater blower is running, that auxilliary fan runs as well.

tanstaafl.