How does olm work and how accurate

[itguy08]

Originally Posted By: CELICA_XX

There is no way it counts engine revs...

This car will sometimes have to idle for 3 hours while parked and the OLM will remain constant.


Sure it can. 3 hours idling at 750 RPM:

3 hours * 60 minutes = 180 minutes
180 minutes * 750 RPM = 135,000 revolutions

3 hours * 60 MPH @ 2000 RPM:
180 minutes * 2000 = 360,000 revolutions

Not all time is the same to your car.

 

[fdcg27]

Originally Posted By: ThirdeYe
I wonder if GM's OLM takes into account length of service? For example, cars that are stored for the winter.


No, GM says OLM zero or one year, whichever comes first, for most applications.
A Volt owner here said that the Volt is allowed to go up to two years, but in the right type of driving, the engine will hardly ever run, almost as though the car were in storage.

 

[GM4LIFE]

Volt owner's manual states 0% or every two years, but the Chevy dealer said they recommend the oil be changed every year due to temperature changes, acid build up, condensation and all other environmental factors. If you store the car in a garage, that's one thing, but if it kept outdoors, I would change the oil once a year. It's cheap insurance.

 

[CELICA_XX]

I have a unique perspective with the OLM here because this car has to idle for hours a day in addition to the normal short trips around town.

For the past three months, with an average of 2.5 hours a day of idling, this car did over 225 hours of idling. That's over 10 MILLION revs just from idling alone.

Then, on my next OCI with a road trip I discover that the OLM still counts at 62 miles per percentage point.

No difference in the OLM rate of decline.



That tells me that the computer completely disregarded all my idle time, because the outcome is the same.

 

[jimbrewer]

The thing I learned from my little experience with the Ford IOLM is that from the standpoint of the oil (not necessarily the engine) is that long runs at operating temperature and relatively low RPMs is like the fountain of youth; I presume this is because the add pack needs time at operating temperature to activate and keep the oil in spec. So, although you consider hours at idle to be bad for the oil, either your manufacturer disagrees, or your hours at idle are "fooling" the IOLM which reads this as a long, slow run on a country road. i.e. really excellent for the oil.

No doubt the math on these things is sophisticated, but since they arbitrarily require a chance at 10K anyway, they can afford to be pretty crude. The end result is not going to be that different for the guy who determines for himself if his service is severe, extreme or moderate.

 

[Quattro Pete]

Originally Posted By: CELICA_XX
For the past three months, with an average of 2.5 hours a day of idling, this car did over 225 hours of idling. That's over 10 MILLION revs just from idling alone.

So what? Where does it say that idling is so detrimental to the oil? Maybe it's not.