8.1 A pressure drop occurred during a cooling system pressure test - NSC Mechanical Technology Automotive - Question 8 - 2021 - Paper 1

A corroded welch plug or core plug can result from prolonged exposure to coolant and the atmosphere, leading to rusting or degradation. The corrective action involves replacing the welch or core plug to eliminate any leaks this issue might cause.

If the pressure is released at a lower pressure than specified for the radiator cap, it could indicate that the cap is defective. The proper corrective measure is to replace the radiator cap with a suitable replacement that meets the manufacturer's specifications.

1. The radiator cap regulates the pressure in the cooling system, maintaining optimal coolant flow and preventing boiling.
2. It ensures that coolant can return to the radiator from the expansion tank, allowing for efficient cooling.

1. A rich fuel mixture can cause incomplete combustion, leading to elevated CO levels.
2. An ignition misfire may not burn the fuel completely, increasing CO emissions.

1. A lean fuel mixture can result in higher combustion temperatures, which can increase NO₂ production.
2. Improper spark advance may cause the engine to operate inefficiently, contributing to higher NO₂ readings.

1. A too lean air-fuel ratio may result in an excess of oxygen in the exhaust gases.
2. Vacuum leaks can introduce additional air into the system, which might also lead to elevated O₂ levels.

1. Ensure that the tester can read the expected pressures of the engine.
2. Clean the sender unit area before fitting the tester to avoid contamination.
3. Inspect the rubber hoses of the tester to ensure they are not damaged or perished.

1. Fuel pressure (suction) before the fuel pump.
2. Fuel pump delivery pressure (after the fuel pump).
3. Fuel-line pressure at idle speed.
4. Fuel-line pressure at high revolutions.

This is necessary to disable the ignition system, thereby preventing electrical shock and ensuring safety when accessing the spark plugs.

Opening the throttle fully allows maximum intake of air into the cylinder, which is crucial for obtaining a correct reading during the compression test.

Recording the readings allows for comparison against the specification readings and noting any differences in cylinder compression, which helps in diagnosing engine health.

The increase in compression from a wet compression test suggests a potential fault in the piston ring or the cylinder walls. Possible issues could include wear or damage that affects compression retention.