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My dad was a motor mechanic on PT boats during WWIII. He said they drained the oil and filled with kerosene and ran the engine until oil pressure dropped and then shut it down, Then, drain the kerosene and fill with oil. Run for 10 minutes and drain the oil again. Fill once again and run 10 minutes and drain again. Fill once again and run and do the next engine. There were three Packard V12 Marine engines in each boat. Beginning of war each had 1200 HP and 1500 HP at end of war under normal conditions. 1800HP under emergency use. (Over revving) That was the procedure for his squadron in the Mediterranean. I thought this would be interesting to a bunch of gearheads.

From internet:
During World War II, the Packard 4M-2500 V12 engines powering US PT boats required meticulous maintenance, often involving flushing with solvent to remove sludge from the oil pan, followed by specific oiling procedures. The Packard V12 engine system typically required roughly 18 to 20 gallons of oil to fill the entire engine and oil tank system, not merely quarts.
WW2 PT Boat Oil Change Procedure (Packard 4M-2500)
Engineers on PT boats, often using a small portable Romec electric pump, followed these steps to manage the oil system:
San Francisco Maritime National Park Association
San Francisco Maritime National Park Association
Drain the System: Old oil was drained from the engine pan and the external oil tank.
Clean Filters: Gas and oil filters were cleaned periodically.
Flush with Solvent/Kerosene: To clean the "mud" (sludge) out of the oil pan, it was common practice to flush the engine with a cleaning solvent (such as kerosene or specialized cleaner).
Run and Drain Again: The engine would be run briefly to circulate the flushing agent, followed by a second, thorough draining of all tanks and the oil pan to ensure all contaminants were removed.
Refill: The system was refilled with fresh, heavy-duty marine engine oil.
San Francisco Maritime National Park Association
San Francisco Maritime National Park Association
+1
Oil Capacity (Packard V12)
The Packard 4M-2500 engines used a dry-sump oil system, meaning the oil was stored in a separate tank, not just the engine oil pan.
Total System Capacity: While specific figures varied slightly by boat builder (Elco, Higgins), the entire system generally held roughly 18-20 gallons (approx. 72-80 quarts) of oil.
Engine & Tank: The 2500 cubic-inch V12 required high-volume, high-quality oil to manage high loads, with regular checks crucial due to their sensitive nature to poor maintenance.