How exactly does the OLM work?

[BritGerCarLuvr]

2 of my 4 vehicles have an Oil life meter. Even though, I religiously change the oil every 5000K following the odometer religiously, I have always wondered how they worked. By the time I roll to "the 5"s" (5000, 10000, 15000 etc...) usually ther may be less than a few hundred mile difference between the OLM and the odometer. Usually the OLM tells me I can "keep on going" for a few hundred more miles. Usually between 750 - 900 depending on which car.) At the oil/filter change I then reset BOTH at oil/filter change.

Car 1. 04 BMW Z4 Sport 2.5i using GC 0W30
Car 2. 04 Benz C240 2.6l using M1 0W40 (for now)

It's pointless on the Jag's as I use the odometer to schedule service.

Surely the engines don't have a "built-in" oil analyzer... LOL

Thank You for helping me understand this topic.

 

[zyxelenator]

There is couple threads about them. Generally there is formula which calculates when it is time to change. It monitors info from temp. sensors, rpm, speed and hours your engine was running. They are pretty accurate.

 

[BMWTurboDzl]

Some of the newer models also measure capacitance. BMW for example is one.

 

[dparm]

Originally Posted By: zyxelenator
There is couple threads about them. Generally there is formula which calculates when it is time to change. It monitors info from temp. sensors, rpm, speed and hours your engine was running. They are pretty accurate.


Pretty much hit the nail on the head. Each company has an algorithm based on the original factory fill and the engine's characteristics, and of course how you've driven it (engine load, temperature, etc).

The less-sophisticated ones are basically just dummy lights that tick down from X miles -- that's why you see guys running way past the OLM's zero mark.

 

[Whimsey]

My wife's 2005 Explorer has a mileage "countdown OLM" system. It just keeps track of the 5,000 mile recommended OCI. It's not a "real" OLM. She runs almost all highway and synthetic oil so the OCI's are greater than the OLM's 5,000 miles OCI.

Whimsey

 

[SteveSRT8]

GM has a surprisingly accurate and respectable OLM setup. It works extremely well on all their V8 engines, but they still have some DI motors that it may be a bit misleading on. A simple reprogram will solve this.

Both of the op's cars have good ones that are known to be effective. I have noticed a lot of BMW owners don't seem to like it, though. It may run the oil longer due to their policy of selling scheduled maintenance with the car.

My 06 Chrysler has a countdown setup, I cannot recommend that one at all.

 

[crw]

Originally Posted By: BMWTurboDzl
Some of the newer models also measure capacitance. BMW for example is one.


Capacitance? (I'm an electrical engineer...)

 

[BMWTurboDzl]

Originally Posted By: crw
Originally Posted By: BMWTurboDzl
Some of the newer models also measure capacitance. BMW for example is one.


Capacitance? (I'm an electrical engineer...)
yep. There is a sensor in the oil pan which measures conductivity between two nodes. There's a PDF floating around on the internet.

 

[SteveSRT8]

Sure hasn't helped them keep engines any cleaner. If you follow their OLM you end up going a LOT of miles between changes.

 

[Quattro Pete]

Originally Posted By: SteveSRT8
Sure hasn't helped them keep engines any cleaner. If you follow their OLM you end up going a LOT of miles between changes.

Has there been an outbreak of sludged up BMW engines lately?

 

[BMWTurboDzl]

Originally Posted By: SteveSRT8
Sure hasn't helped them keep engines any cleaner. If you follow their OLM you end up going a LOT of miles between changes.
Certainly not true for the NA engines of the past, but I concede that the jury is still out on the recent turbocharged offerings (engine codes N54/N55/N63N64).