How does an oil change reminder work?

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Does the computer just turn on the light after the engine has been run so many hundred hours of operation? Or does it compensate for driving conditions, such as decreasing the change interval if a lot of
short-trip driving or hard acceleration is done?
If there's an optical sensor, how does it compensate for some oils being a lot darker than others even when new? Or do they measure the capacitance between a pair of plates immersed in the oil?
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larrymoencurly wrote:

You did not identify a specific vehicle. Different models do it differently. There are some that actually measure crap in the oil. On my newer GM model, the computer simply counts up miles. If you travel less than three miles between startups, it counts the miles against a 3000 mile oil change period. If you travel more than three miles between startups, it counts the miles against a 7500 mile oil change period. This is displayed on the dashboard's Driver Information Center and it shows from 100% down to 0%.
---Bob Gross---
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larrymoencurly wrote:

Im not sure it measures *anything*
I will take hours of operation into account, it should use number of starts. I might use the driving pattern (high revs, low revs).
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wrote:

IIRC the GM algorithm for most gasoline engines is 300,000,000 engine revolutions, minus "penalty factors" for time spent below or above normal operating coolant temperature. Simple as that.
Regards, Al.
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snipped-for-privacy@cogeco.ca mentioned...

Well, if you assume an avg RPM of 2000, then that works out to about a hundred days, continuously running.
I don't have a reminder light, it just says 6 months or 3000 miles.

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Al Haunts wrote:

averaging 3200 rpm. That would have be about 3200 rpm * 60 min/hr * 10 Hr/day * 31 daysY,500,000 revolutions.
I waited till I got home to change oil, but all the Harleys along on the trip got one or two oil changes. If you are right, there is a lot of good oil being dumped out.
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I think the penalty factors likely drag that number down significantly though. You wouldn't see near that amount of time expire between oil changes unless you only drove it on very long trips.
I believe they also say not to leave it over 6 months regardless of what the light does.
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it goes by revs times a factor. it counts revs until it reaches a certain set limit, but the "factor" keeps changing depending on engine condition. when the engine is at normal operating condition, this factor would be 1.0, but when it's cold or overheating, this factor would be greater. someone constantly running at high revs or constantly driving a cold engine (short trips) will therefore get the light on sooner than others. there is absolutely no optical sensor to speak of, and this is pretty consistent across the entire gm line.
the only difference i know of is that the full-size trucks get an engine operating time (in addition to odometer) on their dash, but i don't think it affects the oil change interval system.
what it doesn't do is actually look at the oil, or even know when the oil was changed unless you reset it. if you use regular oil and always remember to reset the light, i guess you can go by the light. if you use synthetic, you could probably get away with letting that light go on 3 times or so between changes, always making sure you reset it as soon as it goes on, of course.
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If I had to guess (And this is a guess) I would say that they use a .... crap what is the word... spectograph (you know the dealy you use in chemestry to shine a light through an opject and it reads how many contaminent entities are flying around...) specrum something... anyways, I would assume that when it gets to a certain percentage it would turn the light on. So much less programming then reading short trips and all, and then it couldn't compensate for outside factors.

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On Fri, 08 Aug 2003 12:53:15 GMT, the renowned "Girgath"

I doubt they use a turbidity sensor, probably just operating hours or maybe f(operating hours, speed, total elapsed time)- kind of an electronic version of the little plastic sticky the oil change places give you.
Of course if someone can point out an oil turbidity sensor as a spare part on a car that will disprove this guess, at least in that case.
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Info for manufacturers:http://www.trexon.com

http://www.gm.com/company/gmability/environment/road_to_future/adv_tech_vehi cles/todays_vehicles/oillife_qa_041603.html
This link says it's an algorithm for GM. Steve
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snipped-for-privacy@my-deja.com (larrymoencurly) wrote:

I think they measure the viscosity of the oil at a certain temperature. From my experience, the oil will get a lot thinner over time.
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I think you all are giving the auto companies too much credit. I doubt they would spend any money on a sophisticated system. Probably just mileage from the odometer...
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Gm cars with efi use air temp, oil temp, number of starts and mileage. I can dig up dissassembly code that shows it in a P4 ( late 80's to ~1998) ecm Pat
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snipped-for-privacy@yahoo.com mentioned...

I agree. But the next Q is, how do you reset the light after you do your own oil change? Do you have to have a fancy terminal to interface wih the OBD stuff on the newer cars? Or can you just do it easily with a jumper or switch?

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Watson wrote:

Different vehicles do it differently. On mine, I push buttons to the DIC to show the oil change life, and then I push RESET and hold it for five seconds. Some vehicles do not have the DIC.
---Bob Gross---
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mentioned...

The ones fitted to vehicles which have long variable service intervals do indeed measure the various parameters mentioned to compute a suitable service interval. They also have oil sensors of some kind that measure the condition of the oil, though this is unlikely to be by viscosity. I know this because I once changed the oil in a Mercedes some considerable time before the computer said it was needed without resetting the service computer. Over the course of a couple of hundred miles the computer increased the service interval it thought was safe, not by a mile or two but by nearly 2500 miles. For this time the computer was actually counting up the milage to the next service, not counting downwards. The BMW 3 is similar but the 5 uses lights that progressively extinguish to the next service.
But the next Q is, how do you reset the light after you do

Depends on the vehicle. Mercedes tell you in the operators handbook how to reset with a sequence of button pressing. BMW can be done with a tool or by grounding a pin in the diagnosic socket.
Huw
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On 8/8/03 2:03 PM, in article snipped-for-privacy@news.inreach.net,

Its different on each car, but I have yet to see one that doesn't explain exactly how to do it, without special equipment, in the owners manual.
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On Fri, 8 Aug 2003 12:03:17 -0700, Watson A.Name - 'Watt Sun'

Again, some yes, some no. It depends on the vehicle.
BMW varies the Oil Service and Inspection Indicator lamp system that uses Mileage, Engine Temperature, and Engine Speed to calculate 'Estimated Mileage' that triggers the lights depending on these factors.
Older fords and Cadillacs used something similar.
I can't remember the last time I saw one that was triggered just with mileage (but I'm sure it was a model before 87).
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GM has a web page describing their system, based on engine run time (total and per start), coolant temp, rpms, and maybe ambient temp as well. I think I remember being told that to clear the light you turn the key on but don't crank the engine, then floor and release the gas pedal three times.
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