I was riding with a co-worker on a work errand yesterday in his F250 supercab 4x4 with the 5.4 V8. Very nice ride. Of course being an oil freak you know I had to ask what oil he used. He told me 10w40 Castrol since it was bought new in 2002. I asked if he ever thought about the 5w20 that was recommended for the motor and he kinda looked at me sideways and told me he'd never heard of it and that 10w40 had worked well for him for many years. I dropped it so I wouldn't seem like a know-it-all, but I wonder if that coice is actually bad for the motor? I asume he's never had a warranty claim and I'm unsure who does his oil changes.