The engine metals are fine. The issue is when you have different chunks of metal at different temperatures. This is particularly problematic when the chunks of metal have different thermal expansion properties, like an aluminum head on a cast iron block. The two chunks of metal expand at different rates, and either one of them warps, or the gasket can't handle the slip between them.I'll disagree with that statement.
The engine metals are perfectly safe up to 300-350F+ as long as the engine oil stays below about 250-275F in the sump.
Most air-cooled motorcycle engines operate in the 275-350F cylinder head temp range very frequently.
Liquid-cooled engines need pressurized Coolant/Antifreeze to stay below the boiling point of the coolant, to prevent hot spots from developing. Once any hot spot develops the whole system can spike quite quickly.
I'll disagree with that statement also.
A 165F thermostat can not compensate for too small of radiator or too slow (or too fast) of coolant flow or too slow of air flow, be it in a KLR or any hot-rodded engine!
I'm not as familiar with air cooled engines. Not my specialty But I could see them running hotter by default and caring less because there aren't coolant passages in the head gasket.
I didn't say 165F thermostats would fix a inadequate cooling situation. I just said it was an old hot rodder solution which gives some extra overhead before the engine overheats. It won't cure a constant overheat issue under normal running conditions.