🔍 Key Concepts

• Diesel engine lube oil system vs cooling water system – how these two systems are normally kept separate • Oil cooler / heat exchanger construction – tubes, shell, and where oil and water flow • Pressure relationships – which fluid is normally at higher pressure, oil or cooling water?

💭 Think About

• Ask yourself: Which option would create a pathway for oil to physically leak into the cooling system, rather than just increasing the amount of oil in the engine? • For each choice, decide: Does this condition actually connect the lube oil and cooling systems, or does it only change quantity/pressure inside the lube system itself? • Think about how a tube or core failure in a cooler would affect where oil can go when its pressure is higher than cooling water pressure.

✅ Before You Answer

• Verify which component directly interfaces between lube oil and cooling water in a diesel engine (usually the oil cooler). • Check which of the listed conditions would allow oil and water to mix across a barrier rather than just build up more oil in the crankcase or lubrication passages. • Confirm that increasing oil quantity or pressure alone cannot move oil into the cooling system without a leak path between the two systems.