As others have noted, engine room blowers are not necessary for diesel engines. And they won't do much good with the engine running since the engine itself sucks more air in than most blowers can suck out.
But if you want one to cool your engine room down quicker then look on Defender for 12V blowers like these: https://search.defender.com/?express...lowers&x=0&y=0
The squirrel cage types are usually more efficient than the in line types. Find a place to place it and hook up a hose to an outside vent you will cut in the hull just below the rub rail. Use a vent cover like this one https://www.defender.com/product.jsp...142&id=1240176
. Wire it to a spare breaker on your DC panel.