Our little VW has served us well for 4 years and over
100000 miles. It never complained and we never had any problems with it.
That is until we took it to Death Valley on a hot June weather (113 F ~
42 Celsius). After an 8 hours drive from San Francisco to the valley the
engine temperature started to raise as soon as we reached the valley. We
stopped and let the car cool off. It took quite some time until we were
able to start again. Next day, same thing happened. We noticed the
overheating always started when we had the AC on and going around 30
miles/h (due to the unpaved roads). We didn't want to stop again as it was
really hot so we stopped the AC, opened the windows and started the heating
in the car. It wasn't very bad to have the heat turned on, because of the
open windows. Anyway, that seemed to do the trick as the temperature of
the engine started going down.
If the same thing happened to you and you decide to stop, don't take off
the radiator cap, let it cool for a while. When you do open it, be very
careful or else you might get severe burns from the hot steam. And if you
have car problems on 190 and stop, do not leave your car especially in the
summer. Better try to make use of the car's shade. The highway is patrolled
by officers, they'll find you.