Grand Marquis LS and 4.6L V8 SEFI OHC Dual Exhaust. Mercury Reliability! Will last forever! If you are looking for a reliable vehicle, look no further than this terrific 2007 Mercury Grand Marquis. J.D. Power named the 2007 Grand Marquis as the highest ranked in Overall Dependability in its class. When you say quality, Mercury comes immediately to mind, and this Mercury Grand Marquis is no exception.