i don't think there's such things as 'life expectancy' for motors. none of them are designed to fail after 10 years or something.
as with all motors, when you're buying a high mileage one make sure it has been properly maintained by the owner. when you talk to the owner and ask him about the car it should become clear to you how much he cares about it.
if you start asking him when he last did this and that and all you get back are 'dunno's or 'i'm not sure what that is' then be more careful.
also factors include -
what KIND of mileage? highway mileage is not as stressful on motors as city. find out if the owner drives to work every day and if its far.
how many owners? generally, the less the better.
if it runs well?
i'd say if you can answer the above questions with satisfactory answers then go ahead and buy it, especially if the price reflects the high mileage.
PS: when negotiating with price don't let on that 'high mileage' may be okay. you need to give him the feeling that you are not happy at all with the high mileage but you're just willing to take a risk if the price is right.
good luck!
