The question is: How old is old and how dirty is dirty?

The GM and oil company engineers have done the testing on this engine for us and have created a system that accomodates the requirements for longevity which produces the answer on the DIC.

I trust that system far more than a calendar and my old eyes on a grayscale chart. YMMV

 

I will take the other path - If the OLM says time to change, then change it, no other time. Case Closed too.

27,000 miles, two oil changes based on OLM and about 5000 miles away from change Number 3. According to the OLM today.

My monthly On-Star report also provides a recommendation for next oil change mileage, again based on the OLM.

To each his own.

 

You are both wrong. GM clearly states what it measures in its OL formula. It has been described in both the owner's and service manuals. You can look it up. They use this formula for every car they produce now. Not just Vettes. The forumula is calibrated for the type of oil recommended, regular or synthetic. The only thing it can't account for is the amount of dirt in the air so that is why they say to change oil using the old pretty much out of date early 1960s guidelines if you are driving in dusty conditions.

Bill

 

Can you guide me to the location/chapter in the service manual that describes this. Apparently, I can't seem to find it. TIA

 

Go here if you want the most amount of information about it. GM OIL LIFE

 

http://www.chevrolet.com/assets/pdf/...upe_owners.pdf

On page 6-25:
"This vehicle has a computer that indicates when to change the engine oil and filter. This is based on engine revolutions and engine temperature, and not on mileage."

Engine revolutions is not only total number of revolutions but at what RPMs the total number was achieved by. An engine can turn over a total of 10,000 revolutions many different ways...1000 RPM for 10 minutes or 10,000 RPM for 1 minute with the latter shearing the oil far more than the former. A top fuel dragster engine only turns over a total of ~600 revolutions during its ¼ mile run but the engine gets to 10,000 RPM during the same run. Engine temperature is not only coolant temperature but also oil temperature. It looks at the absolute max temps as well as the max temp achieved during each start and for how long to make sure all of the moisture is evaporated off. The algorithim is very complete with the exception of being able to monitor dirt ingested into the engine through the air filter/PCV system.

If I had followed any other miles/time schedule, I would have missed my oil needing changed at less than 1500 miles on my ZR-1 when the message appeared. There were quite a few trips to the 7100+ RPM rev limiter during those 1500 miles with coolant and oil temps in excess of 230°F in the heat of a Florida summer. The OLM has also gone to 10,000 miles on my daughter's '99 coupe with easy trips that were long enough to evaporate any moisture in the oil. I've been following the OLM for almost 20 years with zero problems.

 

I found the quoted section in the owner's manual, but was hoping for a more detailed explanation in the service manual.

I have based my oil changes on the OLM since that option has been available. But prior to that, it was a specific time and distance. Both of which are easy to measure and understand by any Joe Blow driver with the aid of a calendar and an odometer.

Because I usually like to understand how stuff works, I tend to ask more questions. So in this case, now that I recognize that temperature plays a part (thanks for the reference) it begs of additional questions. Like what are the ideal temperatures that the OLM system uses? Those answers not only provide oil life longevity, but also engine life if temps can be better controlled.

Anyone have a link to that information? Eric's link is not enough.

 

I would also add to this discussion that whenever the OLM says it's time to change oil, do it, but its also a good idea to include a maximum time interval of one year between changes. On Star will also remind you in the monthly maintenance report if the OLM hasn't been reset in the past year.

 

Well crap, I must have read right over the part where you asked for info from the service manual and proceeded to link the owners manual...sorry about that.:o

The service manual has info about the OLM in Chapter 0 (General Information) in the "Maintenance and Lubrication" section. It basically says it can't detect dust so change it at 3000 miles in dusty conditions or sooner if the OLM says to and not to exceed 12 months. It does say the OLM may say to change the oil before 3000 miles under severe conditions or may go as high as 15000 miles (that's only for 2001 and newer...it's 10000 miles for 1997-2000 and 7500 miles for 1996 and previous). In Chapter 6 under the "Engine Oil Life Monitor Reset Procedure", the various parameters the PCM monitors to determine when an oil change should be done is as follows:
1) Engine speed
2) Engine Coolant Temperature
3) Engine Load
4) Intake Air Temperature
5) Vehicle Mileage

Interesting...I thought it was independent of mileage and I could have sworn oil temperature was monitored too.

There's a guy (Evil-Twin) in the C5 section that I think was in on the design of the OLM and did a nice write-up there...I'll see if I can find it.

 

We may be discussing different criteria for different models and years. My '04 pickup notifies exactly 6000 miles after a reset. i.e. milage based.

My '08 LS3/LS7 service manual has less info about the method of calculation than the owner's manual. I've now scanned every page of all 3 volumes where there was even a remote possibility the info existed.

I read somewhere (maybe here FWIW) that the LS engines were designed to have peak efficiency around a 180-190 ideal water temperature. That temp is also what I've considered to be the ideal for performance since the late 50's, but I don't remember why. Emissions required higher temps, so fans initiate at 199 and are full (90%) at 225.

By not fully understanding oil issues, I used 40 and 50 wt oils in 10-12 qt pans when drag racing in the 60's. The oil co. reps handed out free cases of that stuff just for displaying their decal. We probably would has been quicker by using 10 wt and only 5 qts against their advice.

So ideal oil and water temps, or at least the temps used for the OLM algorithm, would be beneficial to know and be able to better control.