I try to stay out of "Hot Issues", but had to make a comment for this one.
First here is the link that I found
Bob Is The Oil Guy
Second - Disclaimer - I do not work for GM but both my wife's and my income depend on GM.
Third - After reading both sets of links, both people (looks like the same person) make some facts and unbacked statements.
GM's oil life system for the most part is based on dino oils not syn. It bases for determining oil life is based off of a number of factors that most simply listed as Time, RPM, Temperature (internal and external), and which engine. From all of the feedback, and test that I have heard about, it works quite well. These poster claim that GM recommends an oil change at about 1/2 of the oils full useful life whereas I hear that GM allows a large margin of error.
From there these posters have only stated what they believe no facts to back it ether way. The link that Mike posted to the poster states that the only advantge to syn oil is the higher temp rating of the oil quite a few times then starts to change his story a few post in. But reading between the lines I do get the feeling that this person is pushing GM's Oil Life Monitor (which I used until I switched to syn.)
Either way, I feel (from all that I have read and personal use) that syn. oil is a much better oil than dino. It also looks like not all oil is created equal dino or syn. One thing that cannot be disputed is that the oil of today is not the oil of 10, 20, 30, or more years ago. (as well as engines)
From what I have seen on API SM it has made major improvements over the SL rated oil and any newer engine should not have a problem of 5,000+ miles (most current auto manf. recommend oil changes starting at 5,000m) unless servere duty and maybe even then. It also looks like the bigger key to longer oil life is a better filtration system. (The link that Mike posted indicated this when it come to large diesel engines. Then talks about high filtration not being necessary, guess he can't decide)
(A little off subject. In Mike's link the guy is asked about octane level. I one of my meetings with GM there was an engine guy there who did not recommend any octane higher than what is recommened as with current knock sensors are tuned for that grade of fuel. GM and 3 other manf's (Toyota, Honda and BMW) recommend when possible to use a "Top Tier Fuel"
Retailers for best performance and emission ratings.)
I guess in a summary of this, do as you please, if you do not agree with is being said either state you opinion and leave it at that, or state your opinion with proveable facts to back it and then start a valid debate. I for one appreciate Mike's input here since he seems to be the only one with facts. I would also appreciate if there was somebody here (as I am not an oil expert) that could offer a valid other side to this debate since all I can seem to find anywhere on the net is how good (with facts) that syn is and others saying that syn is not necessary, current dino oil is the only way to go, change your oil 3,000 miles, and not back it up with anything other than I have done it this way for a long time without a problem. Which is fine, but I for one would rather keep the money in my pocket over the oil companies and oil producers.
Can anybody give me proven facts that I cannot either use dino oil longer than 3,000mile (or use the GM oil life system), or where syn does not last for 15,000 - 25,000 miles (for the companies that make these claims).
Sorry about this rant, but in my job I deal with the GM Oil Life Monitor and deal with these type of issues all of the time (on a non-technical basis) so hearing it here gets a little frustrating. All I want is FACTS.
Kurt
Edit: Some of this might have come out wrong, but with the way things go with Amsoil on this site and posting right after reading the links, please read this as intended and not as a slam to anyone or any post (past, current or future). Thanks