Personally, I own a 2001 Monte Carlo LS, which uses the same Oil Life
Monitor to determine when is the best time to change the oil. My opinion of
this system so far is good. Twice now I have waited for the Service Oil
indicator before I went ahead and changed it. Now, about 85% of my driving
is highway, usually over 100 kms daily. The other 15% is mostly rural
driving, and every now and then, a bit of city driving thrown in. This car
has close to 180,000 kms, 3.4L, and so far, has not used any oil between
changes, nor is it very dirty when I change it.
Now when I first bought the car a year ago, I didn't know when the oil had
been changed, but it was very clean and the oil filter looked new. Like
you, I was a bit skeptical as to letting the oil monitor decide for me, but
gave it a chance. So I left it and decided I would wait, and finally around
8000 kms, it lit up. I changed the oil very soon afterwards and reset the
system. The second time around was very near the same mileage, under the
same driving conditions. I live in Nova Scotia, where the temperature can
be -30c one day, and +20c the next, and the first oil change was indeed, a
seasonal change. I think it was around November when it was changed. The
car had been purchased in June.
I did alot of research on this system that GM had developed, and apparently,
it looks as though they have spent alot of time and money to develop this
system. In my opinion, it is accurate, based on the results I have seen
thus far with my own GM car. It pretty much does the same job as sending
the oil into a lab technician to have them analyze it, except it does this
constantly by computer/electronics, inside the car, while you are driving.
Another reasoning factor was that most websites explained that todays
engines are far more advanced than those of 20 years ago, when the norm was
to change at least every 5000 kms. It certainly doesn't hurt to change the
oil around 5k, but you are not getting the most out of your oil by doing so.
So, personally, I believe there is no reason not to use the monitor, unless
you are old fashioned and like keeping track of your oil changes yourself.
And there is no problem with that, only that this monitor was designed to
save you from doing so.
Just my 2 cents