There is a lot of air, and the average temperature of the air is suitable for long-term engine operation. It's simply a matter of exchanging the engine heat with enough air. Even liquid cooled engines do this, they use a fluid to move the heat to a radiator and from there into the air. An air cooled engine simply does it directly. It uses fans to circulate a lot of air over an engine structure with fins to provide enough surface area to exchange the heat.
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