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What does it mean when the tachometer shows the engine is 'lugging' at very low rpm under load?
- A.Lugging improves fuel economy safely
- B.The engine is being worked below its effective power range, which overheats and stresses it and gives weak response; a downshift is needed
- C.Lugging is the best way to climb grades
- D.Low rpm under load never harms an engine
Correct answer
B. The engine is being worked below its effective power range, which overheats and stresses it and gives weak response; a downshift is needed
Why
An engine lugged down cannot breathe or cool properly under load and responds with a shudder instead of power. Downshifting to bring rpm back into the working range protects the engine and restores control on a grade.
Manual topic: Shifting - Engine Range · From the General Knowledge practice bank (GK-361).