Keep up proper maintenance such as the coolant changes every two years with additive and it will last forever. The 4.1 was the more troubling engine but they had most of the kinks worked out by the time the 4.5 was introduced. The engine in my Fleetwood was not maintained at all. I don't think the coolant had ever been changed once before I got the car a year and a half ago. It now has 68k miles on it and still purrs like a kitten every time I start it up.