What is the Visible Smoke Test?

• A. A test of fuel economy
• B. A test of ignition timing
• C. A test of engine compression
• D. A procedure that evaluates the emissions from a vehicle's exhaust to determine if it is producing visible smoke.

Answer: (D)

Visible Smoke Test is an inspection where the technician observes the vehicle’s exhaust while the engine runs to see if any smoke is emitted that can be seen with the naked eye. If visible smoke is present, it signals abnormal combustion or burning of oil, indicating excessive emissions and a likely fault in the engine or fuel system, such as worn piston rings, valve seals, a faulty PCV system, or an overly rich fuel mixture. This test specifically looks for visible smoke as a sign of poor combustion, rather than measuring fuel economy, ignition timing, or engine compression. No visible smoke means the exhaust passes this portion, while any visible smoke typically indicates a problem needing repair.