: How exactly do Oil Life Monitors work?

08-17-06, 12:03 AM
My father has a 94 DeVille Concours, and he believes that the OLM bases its % by a 5,000 mile interval. I was wondering what do these OLM base their % on? and how do they do it? and do they differ from say a 1994 N* to a 1996 N*? and do they differ from different vehicles, say from a Cadillac to a GMC?

08-17-06, 04:08 AM
I am only parroting what I have read here and other GM/Cadillac specific boards that are or were frequented by insiders.

The patented GM oil life monitor is specific to each power plant. There is a max. mileage interval built in that varies according to engine design (pushrods vs. OHC vs. OHC with roller cam followers). There will also be a max. calendar interval in the Owners Manual service schedule.

The fundamental baseline data for oil life countdown with the GM system is a count of how many times the crankshaft/camshaft(s) rotate. That basic data point is then adjusted/modified/tweaked by more data such as engine temperature, engine run time, and an exhaustive list of other variables to predict when the oil should be changed (including a substantial safety factor). The details should be in the patent documentation.

Just know that you can trust the system to predict when an oil change is due no matter the mix of driving conditions and styles. I do.

08-17-06, 10:28 AM
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