Engines for vehicle propulsion (840820) cover engines designed to propel vehicles on roads or off-road, including construction equipment. If the engine is purpose-built to drive a vehicle, 840820 applies. Engines designed primarily for stationary power generation or as industrial prime movers, even if physically similar, fall under 840890.

Customs authorities generally look to the manufacturer's technical specification, type-approval certification (such as IMO or USCG marine certification), and the engine's design features — such as corrosion-resistant materials and marine-rated cooling systems. A commercial invoice describing the engine as 'marine propulsion' alone is not always sufficient; supporting technical documentation strengthens the classification claim.