Bert, I have no evidence to support the theory, however, my general opinion is that oil which cannot flow very well will not provide the film necessary to prevent metal to metal contact.

Whether this is true, and at what temperature it becomes true, is the question.

After viewing dino oil at near 0°F., I can picture that it has a difficult time to properly coat the cylinder walls and bearing journals until it warms up a bit. Now, it does not need to warm to 100°F., that is for sure. But, at very cold temperatures, I do honestly believe (without any hard evidence) that there is more wear.

Of course, this would not be evident in a typical climate of California. Another reason that running without a thermostat would not be an issue.