Re: life span of the s197 4.0...
I just hit 36K in mine. It's an 07 with minor mod's so far, all bolt on. I'm an even mix, I try to keep my foot off the accelerator but I also put my foot down more than I care to admit. I haven't had any issues so far except for a fan motor in the dash that was replaced about 10k miles back. She's treated me well so far. But I am putting in a set of 4.10 gear's and a ford racing t-lok next week, just bought them. I'll let you know if that throws anything off kilter.
2007 V6 Mustang w/ Pony Package. Performance Mods - 2.25 custom aluminum catback exhaust with a Magnaflow muffler, AirRaid cold air intake, drilled and slotted rotor's front and rear, SCT Programmer, Ford Racing Tlok, Motiv 4:10 gears, LFP underdrive pulley