IMHO there is little difference in normal operating temp between 0W30 and 5W30 Mobil 1.
The big deal is the modifiers used to get the larger difference in viscosity.
I have run 0W30 Mobil 1 in contours before. I would also consider a 5W20 Mobil 1 or 0W20 Mobil 1 for the winter. Where I live that would be too thin for the summer time.
For the track I would run a straight 30 weight oil like Redline or MAYBE a 10W30.
I wouldn't run any 50 weight oil in a duratec. I have this argument with my father in law all the time.
He has a SBC in a pickup that he runs 20W50 in. The engine has 150K miles on it, leaks like a holy bucket and runs like crap.
He had to rebuild his Stratus' engine due to oil related failure... why? he put 20W50 in it in October and didn't change it until April... startups were hell on that poor car.
My Maxima has 273K miles on it and runs 5W30 just fine it doesn't leak any oil and runs perfectly fine.
My contour has whatever the dealer put in it (I purchased it used and will be putting Mobil1 5W30 in it within the next 2 weeks.
Just for clairifcation
First number = cold viscosity
Second number = hot viscosity
The big problem is when the numbers are too far apart in dino oils... 0W30 and 5W20 oils should be just fine for a duratec that isn't on a racetrack.
