Some interesting details about GM's OLM

[Jim 5]

Here's some particulars of the OLM Algorithym for anyone that's interested.

It's a PDF and you have to zoom in closely to the right hand side corner to see the factors that influence the OLM. I got this from www.goodwrench.com

http://www.gmgoodwrench.com/_res/pdf/OLS1.pdf

 

[MustbetheTG]

great post....

 

[Bryanccfshr]

Everyone should read it.

 

[DakAttack]

I just got an 06 Chevy Express van and I was wondering how this OLM worked. Bythaway do you know if My van has the % of oil life Rem displayed on the dash anywhere, I cant seem to find this option at all. Do the chevy Vehicles even offer this? ...Thanks for the info!

 

[ryansride2017]

I still don't understand why G.M. or any other manufacturer with an OLM can not also program into the algorithym for the light to come on once you reach the highest recommended oil change interval. For example, the manual on our saturn stated not to go past 6k miles per change, but the OLM went off every 7500 miles. Sort of made the OLM useless. The whole system would make sense if they had the light come on at a maximum of 6K miles.

 

[TheTanSedan]

Thank you for posting this. I asked for this insight -- on this board -- about three years ago. Forgot about it, so quite pleased to read it.

 

[Bryanccfshr]

In case the ever PDF dissapears here are some excepts to keep on the server.

OIL DRAIN INTERVAL EXPECTATIONS
Using the GM Oil Life System
¶Highway driving 7,000 to 12,000 miles
¶Urban driving 4,000 to 6,000 miles
¶Trailer towing 5,000 to 7,000 miles
¶Short trip service
(less than two miles) 3,000 to 4,000 miles
¶Typical mixed service 4,000 to 7,000 miles
Actual mileage will vary depending on actual driving conditions.

When the engine
is cold or very hot,
the miles driven
are weighted
more heavily
(penalized)
toward the total
that triggers the
oil change
notification.
The more the
vehicle is used
for short trips or
trailer towing,
the more frequently
the oil
needs to be
changed.
GM test data
shows the Oil Life
System extends
oil change intervals
without risks
to the engine

Vehicle Driving Assessment
Vehicle Testing Oil Analysis
Deterioration characteristics of oil shown are a few of many typically assessed.

Acidity (TAN)
Alkalinity (TBN)
Oxidation Stability
Viscosity Change
Extent deteriorated
Deterioration characteristics

Four different
oil characteristics
were
measured to
determine
extent of oil

Alogorithm

Estimate engine oil
temperature by measuring
coolant temperature

Count combustion events by
measuring rpm
over a fixed time interval

Determine penalty factor based
on oil temperature

Multiply combustion events by
penalty factor

Subtract corrected combustion
events from previous total


Vehicle oil change notification
Combustion event
total less than
amount allowed

 

[TallPaul]

Thanks Jim. Some excellent info. I forwarded it to a number of GM owners. I especially like the table of OCI lengths--nice guideline.

 

[H20024.6L]

This is great info and the first I've seen of the 'insides' of an OLM. I see the value for some, but I don't believe I agree with the first sentence in the first paragraph; "....that assesses engine oil condition..." Assesses the condition of the oil? I'm not sure I agree with that statement, but as I've said before OLM's in their current state are not for me, so I'm biased. When I change the oil and the OLM 'sees the new oil' and 'resets itself', then I'll have some faith. LOL!

 

[XS650]

Quote:

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I still don't understand why G.M. or any other manufacturer with an OLM can not also program into the algorithym for the light to come on once you reach the highest recommended oil change interval. For example, the manual on our saturn stated not to go past 6k miles per change, but the OLM went off every 7500 miles. Sort of made the OLM useless. The whole system would make sense if they had the light come on at a maximum of 6K miles.

---

The manual is what needs to be fixed. FWIW, my 2006 Chevy with OLM says use the OLM or 12 months, whichever comes first. No mention of a change it at xxxx miles, just use the OLM.

 

[Jim 5]

They are guilty of using some incorrect wording when saying it "assesses" engine oil condition. Really, what is happening is that the computer is making a model-based assessment of engine oil condition based on a number of assumptions it has been programmed to make. The program was designed based upon what GM learned about engine oil condition in real-life testing and analysis presumably done after recording all of the variables that are programmed to affect the predicted oil life in the OLM. All of their observations have presumably been used to write the OLM program.

As such, the OLM it really is only predicting your oil condition based on the factors listed in the pdf. That being said, it is important to note the assumptions upon which these predictions are made, namely:

1. You are using Dino oil of the right grade and approvals recommended by your owners manual for your driving conditions;

2. There is nothing wrong with your engine (eg. fuel dilution, internal coolant leak, dirt ingestion etc.)

I think anyone with a GM engine is going to want at the very least to monitor their coolant levels closely and perhaps get a UOA to check (among other things) for coolant in the oil (at reasonable intervals) in conjunction with using the OLM.

 

[ryansride2017]

Quote:

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Quote:

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I still don't understand why G.M. or any other manufacturer with an OLM can not also program into the algorithym for the light to come on once you reach the highest recommended oil change interval. For example, the manual on our saturn stated not to go past 6k miles per change, but the OLM went off every 7500 miles. Sort of made the OLM useless. The whole system would make sense if they had the light come on at a maximum of 6K miles.

---

The manual is what needs to be fixed. FWIW, my 2006 Chevy with OLM says use the OLM or 12 months, whichever comes first. No mention of a change it at xxxx miles, just use the OLM.

---

Agreed. I'm just looking for some agreement between the OLM and manual.

 

[Rickey]

Despite my reservations about computer modeling I still believe that the OLM is more accurate than some arbitrary 6000 mile or other fixed duration OCI. Rickey.

 

[Jim 5]

I agree with Rickey 100%. The OLM is definitely a useful tool for those who want to extend their dino intervals longer, but wonder whether their particular driving habits are compatible with that approach. The standard fixed interval (whether it's 3k, 5k or whatever) does not take into account each person's specific driving habits and conditions. The OLM does this.

I'm going to be interested to note what % useful life my OLM says is left in my oil once I reach the 3k mile point. I did a UOA when the OLM said 10% left(@ 5,013 miles OCI) and the oil condition/wear numbers looked really pretty good.

 

[Matt_S]

Quote:

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I think anyone with a GM engine is going to want at the very least to monitor their coolant levels closely and perhaps get a UOA to check (among other things) for coolant in the oil (at reasonable intervals) in conjunction with using the OLM.

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That's a very broad generalization.

There are only a few engines that had this type of problem and the owners of these engines, as least as far as the population of this board is concerned, know whether or not theirs is one of the troublemakers.

 

[Jim 5]

Matt's right, not every GM engine styles has/had the intake manifold problem. I could have worded that better.

I was trying to communicate that if GM engine is known for intake manifold or head-gasket leaks, you'll want to keep careful track of the coolant.

 

[Jim 5]

No edit function. I meant to say "your GM engine" in line 3.

 

[jorton]

Which GM spec # is for conventional motor oil to be used in OLM equipped autos?

 

[427Z06]

Quote:

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Which GM spec # is for conventional motor oil to be used in OLM equipped autos?

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Do you mean the GM 4718M high temperature specification and the GM 6094M low temperature specification? I'm guessing it's already built into the algorithm according to what the owner's manual recommends. I.e., if your owner's manual recommends SM/GF-4 and GM 6094M, those two specs are factored into the algorithm for your vehicle.

 

[JHZR2]

The OLM in my saab 9-3 is more advanced than the standard GM OLM, supposedly. However, given what I learned about the design of it, it sounds very similar to the standard GM version, per this information given above. I think that mine actually measures oil temperature and coolant temperature, though. On my last trip to pittsburgh, I averaged 37.6 MPG for the whole trip, and the decrease in oil quality from the start to end was 1%/180 miles, inline with the maximum life specced of 18k miles/oil change. When sitting in traffic, or doing a lot of cold starts, short trips, etc., it drops at more of a rate towards 1%/100mi or even down to 1%/75 miles.

So my OLM is calibrated to GM-LL-025-A, and I verified it this past weekend when I documented the life decrease percentage rate.

JMH