I used to work for a cab company a few years back. We had a fleet of Ford crown Vic's, and a few Mercury equivalents. They all had 4.6 motors, and we'd run them till 350k, when we had to legally pull them from service. It was rare when a motor didn't run the distance. Keep in mind our so-called mechanics didn't change oil/filter like they were supposed to. Severe duty recommendation is 5k or less. About the only things that failed were radiators, and fan switches for cooling. We had 5-6 transmissions ready to r&r at a moments ready, but being a taxi, and driving San Francisco hills that's not bad. Same thing for the 2 Lincoln town cars we had in the black car biz. The 2008 blew the plastic intake, the 2001 nothing! My 2000 Eddie Bauer has so far been bullet proof at 99k now.
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