🔍 Key Concepts

• Look at the relative elevations of each expansion tank and pump in the drawing – which pumps are clearly gravity-fed and which might not be? • Think about which system has its own drain tank / sump rather than being supplied directly from a high-mounted expansion tank. • Remember that pumps located above their suction source usually need special priming arrangements or deep-well designs.

💭 Think About

• For each of the four options, trace the flow on the diagram: from the expansion or drain tank, through the pump, to the cooler and back. Which one appears most likely to have the pump higher than its supply source? • Ask yourself: which cooling system is most likely to have its pump located down low in the engine room or crankcase area, making it harder to keep the suction line flooded? • Which system in the drawing shows a return going to a drain tank and then needing make‑up water, suggesting that air could enter and the pump might lose suction?

✅ Before You Answer

• Identify which systems are clearly supplied from a high-level expansion tank (easy natural prime) and which are not. • Verify whether any system shows a cooling drain tank or sump that could be below the pump suction, indicating a need for priming or a deep-well pump. • Before choosing, confirm that your selected system’s pump cannot rely on a simple gravity head line from an expansion tank for priming.