Actually, I think the term is slightly a misnomer.
Radiator cooled refers to the type of cooling that is common in automobiles.
The air-cooled diesel engines are not like an air-cooled motorcycle engine that uses fins on the cylinders. Instead, I think they use internal jackets in the block, similar to water jackets, but circulate engine lubricating oil, instead of water or antifreeze. The lubricating oil is then circulated to an oil cooler that is cooled with air flow from a fan.
I don't know why they are not called oil-cooled!!
I've seen "air-cooled" E/G up to 150KW.
