I'm a big one for manufacturer recommendations - but you can't complain with two vehicles well into the "high mileage" category.
Benefit of diesel oils in a petrol: They're high-detergent, so it'll be clean (and maybe last longer than in a diesel) and designed for more punishment, too.
Thin oils might be for fuel economy - but if they work well (which they seem to, I haven't seen anything about "class action lawsuits" as a result of these oils) then there isn't really all that much to complain about, especially if they can take the car the distance.
I think Shannow can best explain whether there is much difference, and from what I've taken in from his posts is that, bar extremes (like 70 weight oils, or 16 weight oils), most engines don't really care much for what you put in. So long as you aren't creating so much oil pressure as to blow filters apart, of course.
As for Synth. vs Dino: I think this is just technology that can do the same thing for twice as long and reduce the cost of ownership. For most applications, I think either might be okay depending on the drain interval and usage patterns.
For those who "live on the extreme" more with hard driving, short-tripping, turbos and long-drains, then obviously a synthetic oil will be far better suited and cost less than constantly replacing a dino.
For my car - a synthetic oil is where its at. Changing on the older 3month/3K mile (or 5K mile) schedule with good quality conventional would cost just as much as replacing a good BMW LL-01 synthetic once a year/7.5K miles per the 1993 servicing requirements. This doesn't factor in the cost of time if I DIY or the cost of labor if a shop did the work (
Lastly - I wonder what a UOA might show for Rotella in the Toyota Prius. Its definitely something outside the norm, but I would like to see where whether the oil is holding more or less metal-contaminants compared to a thin-synthetic oil of some sort.
A long while back, there was a UOA posted for a recently-model Toyota Yaris using a 15w40 oil here in Australia. The results were certainly quite nice. Again, it was Shannow who pointed out that WARM-UP, not start up is where much of the engine's wear takes place. This is more a product of the oil itself not being able to lubricate and protect as well at lower temperatures, IIRC.
Thanks for your post! I look forward to the ensuing discussion.
You may get lots of comments from nay-sayers, especially with thick oil and a cold climate. But the engines are still working, and presumably not using copious quantities of oil - so who cares?