Originally Posted By: bepperb
Consumer reports did something like that. They saw no differences I believe in Taxi cabs.
Still, where Synthetics shine (turbo apps, sludge prone engines) I haven't seen a good comparison.
Another source of scentific testing that would be the manufacturer specific tests. For example, HTO-06 only a few synthetics pass so obviously there is a difference there.
Agree with above, however to add a little more background, Consumer Reports's study was in 1996 (15years old). CR themselves also noted that their study might not reflect the other benefits and more testing would be intesting (quoted in wikipedia below).
http://en.wikipedia.org/wiki/Synthetic_oil#Advantages
Along those lines, note that there are no other studies in Wikipedia, if a formal scientific study that passes oil nerd scrutiny was done, it would be posted there by oil nerds.
But by the same token, because a study has not been done does not mean the advantages do not exist.
Case in point, the myth on clogged air filters reducing MPG.
This was up for years on fueleconomy.gov government website and based on a 1970s study with carb. engines. This was up until as recently as late 2000s, even though dudes on the net were already speculating it should not apply to fuel injected computer controlled modern cars.
Still, this information was quoted as truth all the time because it remained on the website.
Only perhaps in late 2000s they changed the website saying new study pending, then recently (2009) the Oak ridge national labs finally finished the new study on a modern FI car.
http://www.fueleconomy.gov/feg/maintain.shtml
http://www.fueleconomy.gov/feg/pdfs/Air_Filter_Effects_02_26_2009.pdf
So the point is, that it takes a long time for a study that can pass scrutiny to be done. And things change over the years. If you pony up the couple hundred thousand to run the study properly I'm sure you can get it done, but keep in mind an Oil study will take much longer to cook up than a MPG study.
That being said, it seems with modern chemical engineering, the performance gap between conv. and "synth" is closing, both are now highly processed more that previously and "synth" now comes from cracked groupIII now anyway. By the time your study finishes, there'll be new and improved oils that need to be retested.