Question 85Motor Plants - 1st Asst/Chief

The correct answer is A) The lubricating oil cooler for leakage into the cooling system. When the lube oil sump level is slowly decreasing while underway, this typically indicates a leak in the system. The most likely source of the leak is the lubricating oil cooler, where a breach in the cooler can allow lube oil to leak into the cooling system. This would result in a gradual decrease in the lube oil sump level over time. Checking the lube oil cooler for leakage is the appropriate first step to diagnose and address the issue. The other answer choices are incorrect because they do not directly address the issue of a decreasing lube oil sump level. Option B is incorrect as a standby lube oil pump operating would not cause the sump level to decrease. Option C is incorrect as the tank heating coils being secured would not impact the lube oil sump level. Option D is incorrect as excessive wear on the piston oil scraper rings would not directly lead to a decreasing lube oil sump level.