This heavily depends on the temp range you are discussing.

Lubrication is the least of your worries at certain temperatures. The engine block and pistons being too cold cause problematic expansion and contraction which can lead to block cracks or permanent engine knock issues from what I've seen. This will eventually lead to needing an engine replacement.

It's a trade-off, and nobody seems to have done the science properly - it's just mechanics and engineers guessing which effect is worse.

Is this sarcasm? I can't tell because it is literally the opposite of the truth.

Interesting to me, is that when idling down a hill it does not drop, but if left in gear going down a hill it does drop in temp. It can actually get itself below operating temperature in gear going down a hill. I presume because the heat being pulled out via pumping air through the combustion chamber is greater than the thermostat would allow to be pulled out via the radiator.

Pretty typical of engines of that vintage with hydraulic lifters.

> Interesting to me, is that when idling down a hill it does not drop, but if left in gear going down a hill it does drop in temp. It can actually get itself below operating temperature in gear going down a hill. I presume because the heat being pulled out via pumping air through the combustion chamber is greater than the thermostat would allow to be pulled out via the radiator.

I didn't think that would significant but I could be wrong. Is it a diesel or gasoline engine? My guess would be the thermostat is leaking or wrong temperature.