Oil temp threshhold for engine breakage? (Mainly Merlin engines)

[Crumpp]

he higher you go, the cooler the engines should run, and less likely the chance of damage.

That is wrong.

The higher you go, the less effective the cooling due to pressure and density reduction despite the cooler temperatures.

So while the temperature does get cooler IAW the lapse rate, the density is reduced so we end up with less molecules to transfer heat away from our engine.