Consumer reports found no difference in oil types in New York City taxis (heavy use, lots of miles over a short time). The results are summarized nicely here:
http://www.triumphspitfire.com/Oiltest.html
I remember reading the report a few years ago in the magazine, but can't find it on their web site.
The upshot is that they tried lots of different oils in NYC taxis and ran them 60,000 miles at either 3000 or 6000 mile interval changes, then tore the engines down, and found no significant differences in wear for any oil (regular or synthetic, any brand) or between 3000 or 6000 mile change intervals. This test, of course, doesn't directly apply to cars that are driven on short trips with only a few thousand miles a year, where the age of the oil is more important than the miles. I don't know if anyone has done that test.
Here is another link with a more detailed description of the test (a copy of the original article):
http://www.xs11.com/stories/croil96.htm
It says the test results were published in 1996.
Synthetic definitely flows better at really low temps (important below 0 F), and resists scorching (important if you have a turbo). I don't have a turbo, and I have a garage (even in New England, it isn't below 0 F in the afternoon when I am parked outside), so I use regular oil. I used synthetic in my previous car (before the garage) and it made a noticeable difference in how the car sounded in the first minute after a really cold start. It sounded BAD on regular oil below -10 F, but later on synthetic it sounded perfectly normal at -18 and drove perfectly normal after 1 minute of warming up.
Oil
Linear Mode
