ABYC Diesel Practice Exam

What could be a cause for heavy fluctuation in raw water pressure at high speeds?

1. Low ambient temperature

2. Clogged exhaust riser

3. Correct operation of the seacock

4. Normal engine performance

The correct answer is: Clogged exhaust riser

Heavy fluctuation in raw water pressure at high speeds is often associated with issues in the water intake or exhaust systems of a marine engine. In this context, a clogged exhaust riser can create significant problems. The exhaust riser serves as a conduit for the exhaust gases to exit while also allowing raw water to cool the exhaust. If the exhaust riser becomes clogged, it restricts the flow of water and can create back pressure, which leads to fluctuations in the water pressure being drawn into the system, particularly when the engine is operating at higher speeds. This is because the engine tries to draw more water to keep itself cool and functioning properly, but the clog impedes this flow, causing the pressure readings to vary dramatically. By contrast, low ambient temperature may affect engine performance but not necessarily lead to fluctuating water pressure directly. The correct operation of the seacock ensures a consistent supply of water, and normal engine performance would generally not result in pressure fluctuations unless other issues exist, such as the aforementioned clog.