Sorry for the lapse in time guys. With summer setting in things are getting chaotic at work, not to mention the fact that I have a baby on the way. Anyhow, back on topic, I am a little more cautious when it comes to drain intervals. I KNOW that with most common conventional motor oils the oil life monitor will take you far past the limits of the oil.
(Note, the content below is based on my personal experience with "typical" off-the-shelf oils both synthetic and conventional excluding oils such as Royal Purple and Amsoil as I do not service any vehicles that use it)
I currently have a 2010 Equinox equipped with a 2.4 liter ecotec engine in the shop with 14k miles on it that I am replacing the balance shaft chain and tensioner on. The owner has been going by the oil life monitor and is currently in for their second oil change. The dramatically stretched chain is not a direct result of the extended drain intervals AFAIK
(a service bulletin applies to this model for issues with the chain rattling but the engine design has been around for a decade and this is a NEW issue), but I am inside the motor and see how nasty it has already gotten.
The oil life monitor is still at ~20% and the oil in the engine is mobil conventional (I am not sure exactly of the type as it used to be mobil clean 5000 but that is now discontinued and we buy our oil in bulk stored in large tanks) that meets the standards GM has for this and most other pre-2011 vehicles. (I know this because their first oil change was done at my shop and as a dealer we do make sure the oil we use meets GM's set standards) The oil has is very thin and black in appearance similar to diesel oil, and smells very burnt. The engine is already beginning to develop black varnish on the interior as well.
For me that is just unacceptable for an engine with 14k miles. The owner is not knowingly neglecting their engine as they are following the owner's manual recommendations. But, technically the engine is still being neglected as the oil has clearly broken down and has been so for a considerable amount of time. This is something I see in most engines I perform repairs on AND on a regular basis.
Now, as far as synthetics and especially synthetics designed for extended drain intervals this is less of an issue. There are clear differences that can be seen between the engines using synthetic oil vs. conventional. Still, I find it hard to believe that at least most common synthetic oils can endure the intervals suggested by both the oil companies and auto manufacturers. I do see the differences between engines using synthetic oils and conventional, but not enough to justify the even longer drain intervals. From what I have seen personally, even properly rated synthetics will break down before the oil "needs" to be changed according to (again) both the oil manufacturer and the oil life monitor.
Burn-off is also an issue I see with both synthetics and conventionals when going an extend amount of miles between changes. It seems that once the oil has been in the engine for a certain amount of miles it begins to burn-off more rapidly. The engine may go a certain amount of miles without burning any noticeable amount of oil and then once past that point it will begin burning oil. Many newer engines I see burn a significant amount of oil once past a certain mileage anyway. But, engines that have the oil changed regularly at closer intervals burn significantly less or no oil at all. Again, the difference between synthetic and conventional is very evident in all of these scenarios. But, the synthetics still aren't completely "immune" to the same issues they just perform significantly better.
The bottom line;
Under "real world" conditions synthetics do perform noticeably better than conventional oils in every aspect. However, under these same "real world" conditions, none of the oils I see used regularly will last as long as the oil life monitoring systems indicate. Nor will the "extended mileage" synthetics last the mileage the manufacturers claim. All of this is taking into consideration the auto manufacturers recommendations of changing the oil at least once a year regardless of mileage. Because the vehicles I have based these observations on do accumulate these mileages in under a year's time.
So, based on personal experience with the types of oils indicated above, I do not personally recommend exceeding 3k miles on conventional oil and 5-6k on synthetic. Again, this excludes less commonly available oils such as Amsoil and Royal Purple (which is becoming more readily available, but not popular among the "general" public) and any other "exotic" oils.
This particular topic does relate to motorcycles somewhat, but obviously there are several motorcycle specific oil brands that I have no experience with. But the basics are still there. Synthetic is better, and I recommend keeping drain intervals reasonable.