I'm sure this is an old question, but how in the wide world of sports does my car know how much oil life is left? Is it some sort of sensor? Is it just math? Here at brand T everything made by T is 10k intervals. My Honda does not have a recommended interval, I even read the manual just to make sure. It just says "when oil gauge says 15% life left bring it in". I know the engineers are smarter than me, and I am not questioning the system. Just curious how this voodoo works.
Math.
The math also assumes OE spec oil, not Bob's Mystery Juice.
"Math," meaning a timer/odometer running through a rule-of-thumb algorithm that claims to tell you exactly when your oil needs to be changed.
In reply to Knurled. :
I assume that Honda is using the recommended oil... since I bought their service plan with the car and all.
I figured it would just be math. Also explains why it is over 10k on the odo and the gauge still says 30%, since I drive like a government employee on the clock.
I thought some manufacturers used a conductivity sensor? And IIRC some cars use a rev counter as well.
I recall seeing something on here that said it can be measured by how electrically conductive the oil is or something. I forget who exactly said it, but I'm pretty sure they worked for an OEM.
Edit: looks like ProDarwin is a faster typist than me.
GameboyRMH said:"Math," meaning a timer/odometer running through a rule-of-thumb algorithm that claims to tell you exactly when your oil needs to be changed.
Yeah, usually there is some sort of multiplier that is applied to the odometer mileage, based on the typical driving profile that is recorded by the ECU.
thatsnowinnebago said:I recall seeing something on here that said it can be measured by how electrically conductive the oil is or something. I forget who exactly said it, but I'm pretty sure they worked for an OEM.
It's possible:
https://www.machinerylubrication.com/Read/29407/oil-condition-monitoring
I can't find any solid info on whether any production cars have such a system, I certainly can't find any replacement oil condition sensors. BMW calls their oil level sensor an oil condition sensor, but they do like to give unremarkable parts innovative-sounding names...
GM uses load, speed, temperature, time and mileage into some fancy tables to determine when it needs changed. The one on the Sierra is really close when compared to UOA.
GameboyRMH said:"Math," meaning a timer/odometer running through a rule-of-thumb algorithm that claims to tell you exactly when your oil needs to be changed.
The actual "life monitor" systems take into account number of cold starts, time spent at super high coolant temps, idling, etc. Diesels take into account number of regen cycles too - a truck that suffers from frequent aborted regens might call for oil changes in only 2000mi, maybe even less.
So... math.
Overheat events usually are an instant oil change required now.
A more important question is: how accurate are factory oil life monitors?
More accurate than the sticker they apply to your windshield I would think.
Yup. Math.
It follows drive cycles, average coolant temps, drive time, mileage, yadda yadda. There are some that add a conductivity sensor and (providing it doesn't fail) it augments the algorithm. The problem with the conductivity sensor is that it would only sense things that alter the conductivity of the oil, so for instance things like the evaporation of sulfur compounds might reduce conductivity, metal shavings would increase it, moisture wouldn't really affect it unless there were significant levels of ions dissolved in it... it's hard to use conductivity to pinpoint oil condition.
Appleseed said:A more important question is: how accurate are factory oil life monitors?
Kinda terrible. Probably safe and a bit conservative at the beginning, but over time with increased blowby, wear on the injectors, accuracy of sensors affecting fuel trim, etc could put them squarely in the "useless" category.
Funny. My neighbor was changing his oil and he kept mentioning these percentages too. Had little idea what he was talking about. Late model Impala. 
Appleseed said:A more important question is: how accurate are factory oil life monitors?
Bobzilla, a few posts up, said the monitors are pretty accurate when compared to UOA.
The reminder in my wife's Buick can be manually reset. I haven't read the Owner's Manual, but if they tell you to do it each time you get the oil changed it probably just reminds you at 3000 miles. More of an idiot light than an actual sensor.
My 89 M3 had a five or six bar graph for oil life, it would use a bar or two on a track day but much less with normal driving. I just gave the reset tool away from that car.
Curtis said:Appleseed said:A more important question is: how accurate are factory oil life monitors?
Kinda terrible. Probably safe and a bit conservative at the beginning, but over time with increased blowby, wear on the injectors, accuracy of sensors affecting fuel trim, etc could put them squarely in the "useless" category.
The ones on the Equinox/Terrains are notoriously awful. If you followed them, you'd be changing the oil every 9-10k miles. Except GM says that a quart of oil every 2k miles is normal usage, and they frequently burn above that, so you would be under 2 quarts in the pan, the oil filter would be all collapsed in on itself and wear the timing chains out. And then when you tried to get GM to cover it, they'd look at the maintenance records and say "We recommend every 6k miles. This is negligence, we aren't covering it." Yes, listening to GM's own system would kill the engine and get your repair not covered.
The Nissan ones are just a mileage counter. That's it. You can even go in and change the interval yourself. It just reminds you in say 3500 miles that you are doing for an oil change again. No other logic in place there.
pinchvalve said:The reminder in my wife's Buick can be manually reset. I haven't read the Owner's Manual, but if they tell you to do it each time you get the oil changed it probably just reminds you at 3000 miles. More of an idiot light than an actual sensor.
If it's the same as other GMs, its KOEO and mash the accelerator 4 times. The light should blink a couple times and then go off. There is an algorithm that sets the light. More than just mileage, but as has been discussed it doesn't take into account if you're using Mobil1 or Dollar General oil, the amount of blowby, the climate and road conditions, etc. Big difference if you're using Amsoil in Los Angeles versus using Quaker State on dirt roads in Minnesota.
My 2018 F150 manual basically states "Use the oil life monitor OR 10k miles OR 1 year, whichever comes first." Running full synthetic oil I'm not terribly concerned by that. My oil life is currently reading 34% with 6800 miles on this oil change. Headed for a 10k oil change at that rate.
It also recommends checking the oil level once a month.
NickD said:The Nissan ones are just a mileage counter. That's it. You can even go in and change the interval yourself. It just reminds you in say 3500 miles that you are doing for an oil change again. No other logic in place there.
IMHO the milage counters are by far the most useful.
NickD said: The ones on the Equinox/Terrains are notoriously awful. If you followed them, you'd be changing the oil every 9-10k miles. Except GM says that a quart of oil every 2k miles is normal usage, and they frequently burn above that, so you would be under 2 quarts in the pan, the oil filter would be all collapsed in on itself and wear the timing chains out. And then when you tried to get GM to cover it, they'd look at the maintenance records and say "We recommend every 6k miles. This is negligence, we aren't covering it." Yes, listening to GM's own system would kill the engine and get your repair not covered.
Not bothering to check the oil level (and add if necessary) is just blatant neglect. There are plenty of engines that will consume enough oil while healthy to need a top-off between changes.
rslifkin said:NickD said: The ones on the Equinox/Terrains are notoriously awful. If you followed them, you'd be changing the oil every 9-10k miles. Except GM says that a quart of oil every 2k miles is normal usage, and they frequently burn above that, so you would be under 2 quarts in the pan, the oil filter would be all collapsed in on itself and wear the timing chains out. And then when you tried to get GM to cover it, they'd look at the maintenance records and say "We recommend every 6k miles. This is negligence, we aren't covering it." Yes, listening to GM's own system would kill the engine and get your repair not covered.Not bothering to check the oil level (and add if necessary) is just blatant neglect. There are plenty of engines that will consume enough oil while healthy to need a top-off between changes.
Yeah, but even if you did add oil and such, it was still clearly unhealthy, because the filter media on the cartridge filter would be all plugged and collapsed in on itself.
I have a DI, turbo car. Even if it had an oil life monitor, it would still get fresh Amsoil every 5k.
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