I've told this story before, and it's a personal experience, not a scientific experiment, so I'm not claiming it proves anything, but ....
Originally Posted By: SR5
When I ran thick oils traveling through the Australian outback, it was because it gave me a greater safety margin if things got a little too hot. This was in the old days, so the cars weren't as well cooled or designed as today. The dust and air temperature could heat up a car quick, especially on deep sandy roads . Also before cell phones etc., so less experimenting and more playing it safe. I also carried a Jerry of spare fuel and a second Jerry of water, plus food & tools & blanket etc.
Once I blew a radiator hose on an old dirt road with no traffic. I waited to night fall and the air temp cooled, then I drove until my car was about to overheat and I stopped to let it cool. I kept this going all night until I made it to my uncle's farm in the small hours of the morning. Gave him a bit of a shock as I left about 12 hours earlier and he wasn't expecting me back.
We fixed my car the next day, and it ran completely fine for years after that.
Oil was Penrite HPR 30, the heavy mineral, high ZDDP, 20W-60. It looked after me fine with a dry radiator and a long way from home.