🔍 Key Concepts

• Closed freshwater cooling systems operation and what causes steady vs fluctuating pressure • How air/vapor pockets vs solid restrictions (like clogged impellers) affect pressure behavior • Role of expansion tank level and temperature control devices (thermostats/valves) in changing pressure and flow

💭 Think About

• Think about which condition would make the cooling system pressure gauge bounce up and down rather than stay low or high but steady. • Ask yourself: if the pump impeller were totally clogged, would the pressure fluctuate, or would it tend to stay at one extreme? • Consider what happens if air stays trapped in a closed system—how would expanding and collapsing air/vapor pockets affect the gauge reading as temperature and engine load change?

✅ Before You Answer

• Identify which choice would most likely cause intermittent or cyclic changes in system volume or flow, not a constant restriction. • Rule out any option that would more likely cause a steady abnormal pressure (always high or always low) instead of fluctuations. • Consider whether the issue described would realistically happen as a partial, changing condition (e.g., pockets, surging) rather than a fixed mechanical setting or a completely blocked component.