Those weren't good motors from the feet go but can last as ling as you want them to. Many of those 3.7 motors would have issues if you have ever over heated them. The valve guides are a different metal than the head and can be dislodged when over heated. Same with the 5.7. But really there is no mileage number at which a motor is toast or has problems. They can run a million miles with proper care.