Question 24 MODE01 - Chief MODU Engineer

The Correct Answer is B. ### Why option B (lube oil consumption) is correct: Intake valve guides are lubricated by the engine's oil system (specifically, oil splash or controlled flow). When an intake valve guide becomes badly worn, the clearance between the valve stem and the guide increases significantly. This excessive clearance allows large amounts of lubricating oil, which is present in the rocker arm area and around the valve gear, to be drawn down past the worn guide and into the intake port and combustion chamber during the intake stroke. This ingested oil is then burned during the combustion process, leading directly to a noticeable and often excessive increase in **lube oil consumption**. ### Why the other options are incorrect: **A) cooling water temperatures:** Worn valve guides have virtually no direct impact on the engine's cooling system efficiency or the temperature of the cooling water. Cooling water temperature is primarily controlled by the thermostat, engine load, and heat exchanger efficiency. **C) exhaust temperatures:** While the burning of extra lube oil might slightly alter the combustion chemistry, a worn intake valve guide is not a primary factor in causing excessively high or low exhaust temperatures. Exhaust temperature is mainly dictated by engine load, fuel-air ratio, and injection timing. **D) exhaust pressure:** Exhaust pressure (back pressure) is determined by the resistance of the exhaust system, including the manifold, turbocharger (if fitted), silencers, and piping. Worn intake valve guides do not create a restriction in the exhaust path and therefore do not cause excessive exhaust pressure.