Diesels certainly do run a lot cooler than glows, and we never noticed any cooling issues with engines like AM35s, PAW .19s and ED 2.46 Racers in fully-cowled stunters such as the KeilKraft Spectre. (The only problem with the Spectre was the kit tank, which was hopeless with any engine except the super-tolerant ED Racer!) If I were building one of those old British designs today, for a glow motor, I might consider modifying it to allow a better flow of cooling air. However, the Mercury Crusader, which had no more provision for cooling than the Spectre, suffered no overheating issues that I could detect with an Enya .29-III on 25% castor/5% nitromethane fuel.