How is the engine oil life calculation formulated?

[dave_clt]

I've got 3% oil life left according to my truck message center (and the onstar notification it's sent off to GMC saying I'm due for service.  

 

Sticker on my window says I should change the oil at 6,780 miles and I'm only at 4,750 miles on the odometer.   I think I had first oil change at 1,500 miles (or close to whatever the dealer recommended for that first change).

 

From the manual:

Quote

Engine Oil Life System The engine oil life system calculates engine oil life based on vehicle use and displays the CHANGE ENGINE OIL SOON message when it is time to change the engine oil and filter. The oil life system should be reset to 100% only following an oil change. See “Engine Oil Life System” in the owner manual.

Anybody know exactly how or what the 'calculation' is based upon?   I suspect it's just some algorithm based on elapsed time / trip lengths / mileage and not some fancy sensor that measure particulates, oil density, tachyon particles, etc. 

 

[revrnd]

Just 1 of many items on the 'net about the OLS:

https://www.yourmechanic.com/article/understanding-chevrolet-service-indicator-lights-by-brent-minderler

 

[dave_clt]

Thanks, good info!  Read the manual and searched the forum, but didn't do a simple google, lol.

 

Reading that makes no sense why my % run down so quickly... maybe they didn't reset it after the first change and I just didn't notice.

[revrnd]

Off the top of my head and my I usually got around 8,000 miles on my '04, '11 and now my '17 (all 6 L motors). My 2000 K2500 had shorter intervals during the 4 years I owned it.

[desertz]

Did you make sure they reset the oil life clock (for lack of a better term) when they did the first oil change?

[Grumpy Bear]

Mine is a zero percent no matter what at 7500 miles and nobody drives easier than I do. :-) 

[revrnd]

10 hours ago, Grumpy Bear said:

Mine is a zero percent no matter what at 7500 miles and nobody drives easier than I do. :-) 

I'm pretty sure ambient & engine temps & the amount of time the engine is fully warmed up is part of the calculation. Short trips in winter or engine not fully warmed up would be worse than long light load trips during the rest of the year (moderate temps).

[dave_clt]

13 hours ago, desertz said:

Did you make sure they reset the oil life clock (for lack of a better term) when they did the first oil change?

Hi John,

 

Thought I replied to this earlier but don't see it for some reason.

 

No, I didn't confirm that during my 1.5k oil change; there wasn't any nag light on the dashboard since it was the initial/early oil change.   I typically just look at the window reminder mileage sticker to guide timing.

 

I'll certainly be checking after future changes and watching it more closely in the future.  I don't meet any of the criteria (moderate weather, in Charlotte, usually warm up before driving,) to have the life left go to 3% so quickly 3K after my last oil change (or even if they didn't reset it at the 1.5K change).  Certainly have towed a bit but probably less than 1K of that and ~8,000lb load with  trailer.

 

Ultimately not a big deal if it's accurate or not as I'll track manually, but would like to better understand why it so rapidly decreased.

[sdeeter19555]

I'm pretty sure ambient & engine temps & the amount of time the engine is fully warmed up is part of the calculation. Short trips in winter or engine not fully warmed up would be worse than long light load trips during the rest of the year (moderate temps).

The more I read about the OLM, the more I get the impression there are multiple programs for the same thing in varying vehicle platforms. Mine won't hit the same mileage ever (like it is an actual algorithm) and some hit 7500 miles like clockwork.

Sent from my SAMSUNG-SM-G900A using Tapatalk

[elcamino]

Condition/Concern

 

Since 2010 all GM vehicles have been equipped with the oil life monitor (OLM) system

The monitor calculates the percent of oil life remaining, based on 3 pathways

 

The OLM starts its calculation for all pathways after the first 50 miles to account for marshalling and time before sale.  Subsequently, calculations begin immediately after each reset.

 

Recommendation/Instructions

 

Oil Life Monitor Calculation Pathways:

1.      Engine revolutions- Oil life starts with a fixed number of revolutions and will decrease with each revolution.  Cold / hot coolant temp readings have multipliers that reduce engine revolutions pathway quicker depending on how far from the normal oil temperature the vehicle is operating.

Note: If engine coolant temp gets above 260F, engine overheat condition, the oil life will go to 0%.

2.      Mileage from last reset – Starting with MY 2013, the OLM is capped at 7500 miles for all GM powertrains except the Volt.  In perfect conditions a vehicle would reach 7500 miles from the last reset and the oil life left would be 0%.

3.      Time- This pathway is a liner function, a fixed decrease in oil life for a given time after the oil life is reset.  The oil life will drop to 0% after 1 year regardless of the amount of engine revolutions or how many miles since the reset.

Note: The Volt uses a 2 year timer instead of 1 year. It also uses the engine revolution counter. It does not use the mileage pathway to count down.   

 

[dave_clt]

5 hours ago, elcamino said:

Condition/Concern

 

3.      Time- This pathway is a liner function, a fixed decrease in oil life for a given time after the oil life is reset.  The oil life will drop to 0% after 1 year regardless of the amount of engine revolutions or how many miles since the reset.

 

 

I bet #3 is the reason for mine suddenly dropping to 'due' for an oil change.  I found my email confirmation from my last service / oil change.

Appointment Details

Saturday, November 5, 2016 9:00 AM Mileage 1,750

[jerryw1000]

9 hours ago, revrnd said:

Short trips in winter or engine not fully warmed up would be worse than long light load trips during the rest of the year (moderate temps).

Yeh.......once a week on Sunday evening I drive mine 1/4 of a mile from the house down to the road to put my garbage can out........mine drops 2% on the 1/2 mile round trip.

[Black02Silverado]

20 hours ago, Grumpy Bear said:

Mine is a zero percent no matter what at 7500 miles and nobody drives easier than I do. :-) 

Our 16 Suburban does the same thing.  0% = 7,500 miles.  Every time.   Our 2011 Acadia was 0% = 5,000 miles every time.  Up to the 90k miles we had it and traded in on the Suburban.

[redwngr]

The more consistently a vehicle is driven, the more likely the olm, will trigger at the same mileage. 

 

If a vehicle gets different usage during some oil change cycles it is more likely to trigger at a different mileage. 

 

 

And of course that's the whole reason the OLM system was developed.  

 

And yes is is an algorithm and is not an oil sensor.

 

 

 

[Grumpy Bear]

12 hours ago, elcamino said:

Condition/Concern

 

Since 2010 all GM vehicles have been equipped with the oil life monitor (OLM) system

The monitor calculates the percent of oil life remaining, based on 3 pathways

 

The OLM starts its calculation for all pathways after the first 50 miles to account for marshalling and time before sale.  Subsequently, calculations begin immediately after each reset.

 

Recommendation/Instructions

 

Oil Life Monitor Calculation Pathways:

1.      Engine revolutions- Oil life starts with a fixed number of revolutions and will decrease with each revolution.  Cold / hot coolant temp readings have multipliers that reduce engine revolutions pathway quicker depending on how far from the normal oil temperature the vehicle is operating.

Note: If engine coolant temp gets above 260F, engine overheat condition, the oil life will go to 0%.

2.      Mileage from last reset – Starting with MY 2013, the OLM is capped at 7500 miles for all GM powertrains except the Volt.  In perfect conditions a vehicle would reach 7500 miles from the last reset and the oil life left would be 0%.

3.      Time- This pathway is a liner function, a fixed decrease in oil life for a given time after the oil life is reset.  The oil life will drop to 0% after 1 year regardless of the amount of engine revolutions or how many miles since the reset.

Note: The Volt uses a 2 year timer instead of 1 year. It also uses the engine revolution counter. It does not use the mileage pathway to count down.   

 

Point #2. I must be perfect. Cool I like perfect. 

Point #1. Yea, I drove her in M5 for over a month simulating the 4.10 gear and the change was still nothing. I installed a 170 F thermostat and that has had zero effect. Still 7500 miles. 

Point #3. I put 45K on in a year. Don't think I run the timer down. LOL