Look, the movie they made about PT-109 might be a problem. I don’t know if the story is true or not. In the movie the 109 is afloat drifting with out power I think it is even stated that they have no fuel. I could be wrong. To even confuse things further the boat catches on fire and their is oil fire all around the 109. How do you have an oil fire if there is no fuel on board?
They burned high-octane gas, not oil. And with all three engines running you could only go 6 hours. Typically only one engine would be run to preserve fuel and decrease the racket of the 3 V-12 engines. The night of the sinking they were idling one engine and in position with at least two other boats spread over several miles.
One possibility for the oil fire is that PT boats had smoke generators on many of the hulls to provide a screen for quick withdrawal. A boat could be out of fuel and still have oil in the drums.