Question 13 MODE01 - Chief MODU Engineer

The Correct Answer is C **Explanation for Option C (Excessive lube oil consumption):** Worn intake valve guides create an enlarged clearance between the valve stem and the guide. This excessive clearance allows a significantly increased amount of engine lubricating oil, which is present under pressure in the cylinder head and valve train area, to be drawn or sucked past the valve stem and into the intake port and combustion chamber during the intake stroke (when the cylinder is creating a vacuum). This oil is then burned during combustion, leading directly to excessive lube oil consumption. **Why the other options are incorrect:** * **A) increased engine breathing efficiency:** Worn valve guides do not improve airflow or volumetric efficiency (breathing efficiency). In fact, the resulting carbon deposits and potential poor valve seating (due to the valve not being held precisely) can actually slightly decrease efficiency over time. * **B) excessive valve lash:** Valve lash (or valve clearance) is determined by the adjustment of the rocker arm or tappet and the components in the valve train (pushrods, lifters). Worn guides affect the lateral stability and sealing of the valve stem, not the vertical clearance (lash). * **D) lower than normal fuel consumption:** Excessive lube oil consumption typically leads to fouling, smoking, and deposits, which are signs of inefficient combustion. While the engine might be burning a negligible amount of "oil as fuel," this does not result in a measureable decrease in overall fuel consumption. The primary and significant consequence is increased oil consumption, not improved fuel economy.