Let's say you get your oil changed but the monitor (on screen) doesn't get reset. Now, according to the information center, you have 30% of life left on your oil. Doesn't the oil get checked each time you start your car? Why doesn't that monitor get updated automatically?
Do I have the whole concept of this oil monitor all wrong? Does the percentage of life get based on mileage or time since your last reset?
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Sal, the Oil Life Indicator (or OLI) gets reset when you manually reset it. The procedure is slightly different for any number of models, but the theory is the same.
The OLI is not connected to your drain plug or anything, so it doesn't know that you've changed the oil. It's based on a computer algorithm that calculates the usable life of the oil based on a number of factors since the OLI was last reset, like number of engine revolutions, coolant temperature, duration of ignition cycles, ambient temperature, etc. It's actually pretty accurate. If you drive 2 miles each trip in the dead of winter, it might tell you your oil is expired after 1500 miles (and it probably is if you drive very short trips).
It's a much better solution than a flatline recommendation of 5000 or 7500 miles.
I tend to just go with what I've lways done, That is I change the oil and filter every 2000 miles regardless of what the oil life indicator says. I do this with all my vehicles except motorcycles. On motorcycles I do the change every 1000 miles. It's a little overkill maybe but all of my motors are spotless inside and out even the high milage ones.....Caddy 154'000...Mercedes 100,000...Harley 80,000, Van 170,000. The oil life indicator is kind of a cool gadget but I don't thik it's meant to be an accurate tool in the real world. ( More of a...Hey Grandpa, Don't forget to change the oil again thing)
Sure, it never hurts to change the oil more often. But do keep in mind that the OLI was developed over years of research and development and is very accurate at estimating the oil life based on the type of driving you do. That's the key to remember -- "based on the type of driving you do". I always change my oil when the OLI is between 10 and 20%, although a good amount of reserve is built-in.
If you drive on Interstates in the summertime, you can see a change interval of upwards of 8000 miles or more...simply because at those driving conditions, you're really not degrading the oil at all. It just costs more money to keep changing it if you don't need to.
Again, it never hurts to change it more often, but it's designed to "predict" your estimated oil life based on your driving and the environment. In some cases, 2000 miles may be too long to wait to change it. In most cases 2000 miles is much too often to change it. In my case, I'd be changing it once a month with a 2000 mile change interval, so I follow the OLI pretty closely.
It was validated on the Northstar powertrain, but is now used on many many GM platforms (trucks, Corvettes, Northstars, etc.).
It usually works out to about once a month in each of those vehicles anyway. The motorcycle is the possible exeption. My caddy is a '91 and I just never have been to confident in that particular system. I have done oil analysis testing before and that has shown some interesting results....One case in particular was that the OLI was reading 0% at 1800 miles I drained the oil and sent out a sample for analysis and the oil was fine, No breakdown in viscosity and very little contamination ( Which I attribute to the oil change overkill ) I obviously could have run that oil quite a few more miles as you say, But I've always enjoyed long life and great performance out of my vehicles doing it this way so I'll probably continue the trend.
Wow! Great, great explanation! I completely understand the process now.. I actually used to change my oil when the OLI was at 40%.. I guess that was a waste.. It sounds to me that 20% would even be overkill... I just don't think I could mentally go any further than that.. I'm probably wrong for thinking that way...
That is interesting -- about the OLI expiring at 1800 miles and an analysis showing still good. I'm sure that when it was designed, it was designed to err plenty on the conservative side, in case of any engine damage due to that OLI and a following lawsuit...
But you're right...there's obviously no harm in changing it SOONER than the OLI says.
I seem to remember that when the car was new I asked the service manager at St. Claire Cadillac here in San Jose, Ca. about the OLI and at the time he said something like I was saying earlier in this thread. The OLI was sort of a reminder rather than a realistic indicator of oil condition. That being said, technology moves along sort of quickly and they're probably much better 12 years later ( As in NOW!) But this is what these sites are for, So we can all discuss this stuff and benefit from our collective experiences.
I use the OLI as a guage to change my oil. My Caddy is pretty much a garage queen, but I get the urge to drive it when the weather is nice. I use the same rule of thumb that jadcock uses, change between 15-20% life left. I used the quick change place at the Cadillac dealer the first time, but with 8 quarts and $40.00 I decided I would do it myself or let my shadetree mechanic do it.
I don't know if any of you have the leaking North*, but I do. I find a small spot on the garage floor, and do not need to add oil between changes. Its a minor inconvience considering a new seal involves breaking the engine in half to get to the gasket. Estimated cost is $1,500-$2,000 for that little job. I can live with the small leak.
I think I had that new seal put in when my car was still under warranty! If that was the same thing, then it had gotten worse.. I wish they would fix this problem. How is it on the new Northstars? Actually.. I will create a new topic regarding this matter. I think many people will notice the title and check it out...
Oil Monitor Question 
