As i log my motor temperature with my eagletree datalogger i just looked through some previous logs and this was the one with the highest temperature reading. actually 73,7 C (164.6 F) and not 70 C (158 F) as i stated previously.
you have to look at the gray curve. It startet with 42 (107.6 F) and while driving it rose. I had to make two short breaks as some guys came up with their dogs. These are the most critical moments as there is no airflow anymore. Therefore you can see the highest peak on my second break 73,7 C (164.66 F). As i started driving again the temperature sank back to 65 C (149 F).
Outside temperature was around 29 C (84 F).