46 CFR §119.420

1. (a)Except as otherwise provided in paragraph (b) of this section, all engines must be water cooled and meet the requirements of this paragraph.
   1. (1)The engine head, block, and exhaust manifold must be water jacketed and cooled by water from a pump that operates whenever the engine is operating.
   2. (2)A suitable hull strainer must be installed in the circulating raw water intake line of an engine cooling water system.
   3. (3)A closed fresh water system may be used to cool the engine.
2. (b)A propulsion or auxiliary diesel engine may be air cooled or employ an air cooled jacket water radiator when:
   1. (1)Installed on an open deck and sufficient ventilation for machinery cooling is available; or
   2. (2)Installed in an enclosed or partially enclosed space for which ventilation for machinery cooling that complies with the requirement of § 119.465(b) of this part is provided, and other necessary safeguards are taken so as not to endanger the vessel.