Running Engine Blowers

Yeah, but the problem on normal sized yachts is you have limited resources (electricity), both from shorepower and generator. If you have large blowers exhausting from the engine room, you can get the temps down in the engine room within an hour or two to respectable levels or not much higher than ambient temperature once the motors are turned off.

Sorry if this has been said but, diesel engines are rated for sucking in a certain amount of air... Which happens to be a lot at high rpms if I'm not mistaken, and not turning on the fans could lead to the engine not running properly, because it's starved of air. I suppose you observe the exhaust for signs of there not being enough air, at whatever rpm you are running at normally; black smoke being the biggest indicator, no good, turn the fans on.

You will also find that the hotter the intake air the hotter the engine will be in general particularly with NA engines and it does occur in after cooled engines as well as the air charge is only exposed to the cooler matrix for a certain duration so optimum cooling does not always occur especially if there is some growth on the tubes/plates that inhibits the full heat exchange forseen by the system designers who also no doubt indicated a maximum inlet temperature for a good reason other than a few more words in the manual.