How is Oil Life determined?

[l008com]

How does my truck determine my oil life?

I drive less than 10,000 miles per year. And my truck takes a full year to tell me I need an oil change. Now I do use high mileage full synthetic, so it's probably fine to go that far. But I do feel like it "feels" a little smoother after an oil change.

So I do less than 10k but I certainly do more than 3k. I just looked at some old paperwork and it looks like I've been doing roughly 6k per year. Is it just milage based? Or somehow RPM based? Or does it somehow 'sense' the qualities of the oil and it just knows when they've gotten too bad?

 

[TollKeeper]

The OLM (Oil Life Monitor) is based on counted engine rotations.

Is also NOT recommended to use that as guide for oil changes.

 

[l008com]

Why are you not supposed to use that? Can you elaborate on that?

 

[littleblazer]

It's a really complex timer that accounts for various properties... lab tested. I tested the one on my I6 against an oil analysis and it was still conservative at 13k miles... I don't know if the old ones have a one year timer though. Regardless of mileage, change it once a year if you're only doing 5 or 6k miles.

Put another way, changing it more frequently won't ever hurt anything.

 

[l008com]

I would never go MORE than a year. I could potentially go back to twice a year. The oil I use says it's good for 10k. So changing it after 3k seems excessive. That said, if the engine runs smoother changing it at 3k, I'll probably do that.

When I changed the oil the other day, it was dirty but otherwise seems smooth and oily, not chunky or sticky or anything.

 

[cornchip]

The OLM (Oil Life Monitor) is based on counted engine rotations.

Is also NOT recommended to use that as guide for oil changes.

I'd also agree with rotations.

The OLM (Oil Life Monitor) is based on counted engine rotations.

Is also NOT recommended to use that as guide for oil changes.

I can verify that it must be based on RPM. I know this since I had lost my OD in April of 2018 and just used 3rd from then on. My oil life percentage dropped rapidly, especially on the highway where I limited myself to 70mph. The 4200 handled it like a champ.

 

[Ilikemy3s]

The way it was explained to me .. ..

The OLM uses a formula taking into account "number of times you start the engine" and takes that and figured in run time, mileage driven during said run time RPMs during said run time, as well as RPM changes from low to high. And then it calculates the overall perceived life of the oil based on standards it goes by.

Keep in mind that it was once thought of that steady highway mileage (like an over the road sales man ) was considered easier on an engine while stop and go like a city taxi or police car was considered sever duty. So steady highway mileage daily would give you longe oil life. One year I put almost 25k miles on my Envoy but that was family trip from NJ to Disney and other places. And I averaged 12k on the OLM

And when these trucks were in the dealers new, GM was willing to base their engine warranties for 5 years with the OLM the way it is set up, it cant be all that bad.

I dont go til the OLM light comes on any more. And yes, changing oil ahead of time wont hurt it.

242+ K miles on my original engine and still going strong.

just my thoughts

 

[Mooseman]

The OLM is pretty good at estimating when the oil needs to be changed unless it's severe duty or if not enough use and it goes over a year to reach it. I think the reason the manual will say at least once a year no matter the OLM or mileage is because of perceived condensation, acid formation and the breakdown of additives over time.

I have to admit that I have gone over a year on the TB since it gets little use nowadays. And the myth of going over a year on old oil within the mileage was dispelled by Project Farm.

So if you are over a year on your current oil change but within the OLM and mileage, there's no problem to keep that oil in there but if you want to change it out anyway, that's fine too.

 

[TollKeeper]

If I used the OLM for my wifes car, we would be changing the oil every 3 years!

On my Envoy, I would be changing it every 10 months. I dont know the miles..

I usually change my oil when my OLM gets to 35%

 

[Redbeard]

For piece of mind send an oil sample to Blackstone and for a couple of extra bucks they will tell you how much life is left in the oil if you feel the need to get maximum use out of your oil. Go to https://www.blackstone-labs.com/ and order a free container to ship your oil sample to them. I have used them on and off for many years and it is good to know when there aren't extra liquids (fuel or antifreeze) and metals floating around in the oil that shouldn't be there.