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#4466288 - 07/21/17 03:14 PM 2016 Cadillac CTS-OLM at 60% after 900 hwy miles!
hal26 Offline


Registered: 11/17/04
Posts: 68
Loc: Texas
Bought 2016 2.0 Turbo CTS with 1,036 actual miles and 13 months old. Elderly lady passed away not long after buying the car. Oil Life Monitor was at ZERO. I figured lots of very short trips to the store,doctor etc. I immediately changed the oil/filter myself using Mobil 1 in the proper viscosity. This is now my wife's car and it is her weekend toy. She drives it typically 40 miles a week on the highway and no short trips. Pampered garage queen. I was shocked when the OLM read 60% oil life remaining after only 4 1/2 months and 900 highway miles using top tier premium fuel as well. My wife is 62,drives conservatively,rarely stuck in traffic and little time idling. so the turbo is rarely active and she does not creep around slowly in it - ever. I'm wondering if the OLM would start ticking down to ZERO if the OLM was reset and the car was parked for 12 months (the recommended time between changes)and was not driven a single mile.
Seems like a big waste of expensive oil to change it at around 2,500 miles which is when it will be down to ZERO at the going rate. My question is: Does the OLM use time as one of the major determining factors when calculating oil life?


Edited by hal26 (07/21/17 03:15 PM)
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#4466309 - 07/21/17 03:28 PM Re: 2016 Cadillac CTS-OLM at 60% after 900 hwy miles! [Re: hal26]
Danh Offline


Registered: 10/16/10
Posts: 1750
Loc: .
With those two data points is sure looks like the IOLM uses time as one of the factors. Like most OEMs, GM requires an oil change at least once per year, regardless of miles. And 4 1/2 months is about 40% of a year. Given the general cluelessness of the automotive public about such things, it would make sense to include the time element in the IOLM calculations and maybe GM has done so.

It may seem a waste to change oil after only 2,500 miles, but to preserve the warranty it's probably necessary.

If it's an IOLM that counts down in single digits you could take a before/after look if the car was unused for a several days: 4 days should knock the remaining oil life down by a percentage point if time is in the algorithm.


Edited by Danh (07/21/17 03:31 PM)

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#4466313 - 07/21/17 03:32 PM Re: 2016 Cadillac CTS-OLM at 60% after 900 hwy miles! [Re: hal26]
zfasts03 Offline


Registered: 07/21/08
Posts: 253
Loc: Bucks, PA
If time has been added to the OLM it is news to me. I know for certain that on 2003 and 2012 GM (Corvette) vehicles time alone does not deplete OLM. Just that the owner manual states if the OLM does not come on in 1 year to change oil and reset.

Possibly time has been added for newer GM vehicles, but this is news to me.

Newer Mercedes Benz vehicles, time does diminish OLM.
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#4466316 - 07/21/17 03:34 PM Re: 2016 Cadillac CTS-OLM at 60% after 900 hwy miles! [Re: hal26]
oil_film_movies Offline


Registered: 06/13/16
Posts: 2569
Loc: MN
That is wierd. To answer your question directly, the GM OLM algorithm appears to NOT take into account time.
It does have a maximum miles number in it though.
It basically counts engine revolutions, then penalizes "rough" revolutions (cold, high-RPM, or high load blowby) more.

One more thing: I notice the algorithm immediately orders an oil change if the coolant temperature is way high, no matter what.

Lets take a look at it:

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#4466325 - 07/21/17 03:39 PM Re: 2016 Cadillac CTS-OLM at 60% after 900 hwy miles! [Re: zfasts03]
oil_film_movies Offline


Registered: 06/13/16
Posts: 2569
Loc: MN
Originally Posted By: zfasts03
If time has been added to the OLM it is news to me. I know for certain that on 2003 and 2012 GM (Corvette) vehicles time alone does not deplete OLM. Just that the owner manual states if the OLM does not come on in 1 year to change oil and reset.

Possibly time has been added for newer GM vehicles, but this is news to me.

Newer Mercedes Benz vehicles, time does diminish OLM.


I was thinking the same thing. It seems GM could easily add a "max time" to the flow chart shown above. It does seem cars like BMW, Mercedes, mabye Ford's IOLM too, do incorporate a max time.

Related to this, I would like to know the Max Miles allowed, as it does seem to be part of the algorithm reported from https://etda.libraries.psu.edu/files/final_submissions/392
And maybe the max coolant temperature that triggers an immediate oil change light.

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#4466329 - 07/21/17 03:41 PM Re: 2016 Cadillac CTS-OLM at 60% after 900 hwy miles! [Re: hal26]
zfasts03 Offline


Registered: 07/21/08
Posts: 253
Loc: Bucks, PA
It makes sense that time is a factor, but doesn't look like GM takes that into account.
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#4466330 - 07/21/17 03:43 PM Re: 2016 Cadillac CTS-OLM at 60% after 900 hwy miles! [Re: hal26]
DoubleWasp Offline


Registered: 05/21/12
Posts: 5236
Loc: Fort Lauderdale, FL
Maybe it's one of those engines that lives best when it gets smacked around a little, and it isn't getting that from your wife?
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#4466351 - 07/21/17 03:56 PM Re: 2016 Cadillac CTS-OLM at 60% after 900 hwy miles! [Re: hal26]
oil_film_movies Offline


Registered: 06/13/16
Posts: 2569
Loc: MN
We can infer, based on the flowchart, how it calculates the percent life remaining.
It is MIN(miles/max_miles,revs/max_revs) expressed as a percent.
(Note the "revs" is really a modified, penalized rev count.)

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#4466357 - 07/21/17 04:02 PM Re: 2016 Cadillac CTS-OLM at 60% after 900 hwy miles! [Re: hal26]
Eddie Online   sleepy


Registered: 12/07/03
Posts: 9568
Loc: Florida, Cape Coral
Are you sure your wife isn't sneaking off to the drag strip?
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#4466374 - 07/21/17 04:22 PM Re: 2016 Cadillac CTS-OLM at 60% after 900 hwy miles! [Re: hal26]
pbm Offline


Registered: 04/19/04
Posts: 7605
Loc: New York
The only vehicle I've owned with the GM oil monitoring system was my Chevy Cruze and it definitely DID deplete with time even if not driven....approx. 10% a month. I bet that's what's happening with your Caddy...
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#4466379 - 07/21/17 04:26 PM Re: 2016 Cadillac CTS-OLM at 60% after 900 hwy miles! [Re: hal26]
Coprolite Offline


Registered: 07/03/11
Posts: 1224
Loc: Houston, TX
My former 2012 F150 EB would run down based upon time or miles. However, if you tore off 3-500 miles after it had sat for a while, it would use the time based deterioration that was previously there. In other words, if you let it sit and lose enough %, the long trip would "mysteriously" not use another % at all. I never got too deeply into it, but time was one boundary and mileage seemed to be the other boundary mathematically. After I confirmed that, I didn't try to see if other factors had any sway in the calculations since I could always do the best case/ worst case comparison when planning OCI.

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#4466440 - 07/21/17 05:23 PM Re: 2016 Cadillac CTS-OLM at 60% after 900 hwy miles! [Re: hal26]
Ammofirst Offline


Registered: 06/22/17
Posts: 353
Loc: Western usa
No doubt That's seems excessive. Maybe a call to GM is in order to determine if they have in fact introduced a time factor into their olm. We have that engine in our Buick Regal. Every time I change the oil it reeks of gas ⛽️ You seem like a car guy, have you looked into The characteristics of this engine ?

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#4466457 - 07/21/17 05:36 PM Re: 2016 Cadillac CTS-OLM at 60% after 900 hwy miles! [Re: hal26]
SirTanon Online   content


Registered: 06/23/14
Posts: 2158
Loc: Phoenix, Arizona - USA
Any chance it adjusts calculation based on history? If it does, then it may be taking into account that the last owner barely put any miles on it in the previous 13 months, and extrapolating the time/mileage from that into the current fill.
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#4466462 - 07/21/17 05:44 PM Re: 2016 Cadillac CTS-OLM at 60% after 900 hwy miles! [Re: SirTanon]
oil_film_movies Offline


Registered: 06/13/16
Posts: 2569
Loc: MN
Originally Posted By: SirTanon
Any chance it adjusts calculation based on history? If it does, then it may be taking into account that the last owner barely put any miles on it in the previous 13 months, and extrapolating the time/mileage from that into the current fill.

That would make sense. It matches what gets recommended to people on bitog all the time. Somebody will write in, say they forgot to change their oil for a long time, and they ask "what should I do?". The advice is often "Run a decent dino oil for 3k miles, change, and then proceed on normal OCI's".

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#4466486 - 07/21/17 06:05 PM Re: 2016 Cadillac CTS-OLM at 60% after 900 hwy miles! [Re: oil_film_movies]
hal26 Offline


Registered: 11/17/04
Posts: 68
Loc: Texas
Thanks guys for all your helpful insight,much appreciated. I owned 3 C5's and one C6 Vette over an 18 year period and the OLM's never ran down based on time. I averaged about 4K per year in those.
One thing I failed to mention is that we are out in the Central Texas hill country and the weather is mild all year except in the summer when 100 degree temps are not that uncommon. Still 95% highway and no trips or short hops. It has got to be time based.....
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