I've run Synthetics and conventional oils in the same engines and done the UOAs.
Everytime, the UOAs with same OCI the conventional shows lower wear numbers.
As far as MPG (which I keep track of better than anyone else) NO difference in a V6, I4 or V8 engine driven by the same person over the same routes.
As far as keeping a clean motor, NO difference IF you change out your oil per mfg manual.
As far as long life of engines, I've gotten almost 300k out of my 1985 Jetta (it's around 295k right now) and it's running great! My 1996 Chev truck just went over 200k with ease and is running great.
My 2000 chev truck had a leak on it's valve cover and was spotless inside.
My 1999 Ford Taurus at 61k and 108k had to have head gaskets and was spotless inside.
All they have seen except a few test OCI of syn was Pennzoil, Castrol or Halvoline/Chevron all under $1 a quart.
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What about when synthetic costs the same as dino? I have a stash of M1/M1EP, PP, & ML Syn, that averaged less than a $1.50/qt.
Rebates are the cost equalizer. When cost is no longer a factor, synthetic wins (IMO).
I've got hundreds of quarts of oil that I bought @ 49 cents a quart.
You oil is 3 times the cost of mine.
Cost is always a factor...
Plus, the UOAs don't lie.. Lower wear with Conventional oil over Mobil 1 in my Chev truck and Toyota corolla.
Plus, it's a lot harder to find Syn around $1.50 than conventional around $1.50 a quart.
Take care, Bill