How does an oil change reminder work?

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).

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.

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.

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

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.

Best regards, Spehro Pefhany

I read that the BMW computer monitors number of starts, time elapsed, miles, engine temperature reached etc to compute when oil change is needed.

A computer chip monitors, the number of starts, RPM's, running hours, engine temperature, (and a fifth parameter which escapes me at the moment,) and does a calculation then illuminates the light.

mike hunt

larrymoencurly wrote:

Though the manual for my car claims the service light comes on based on severity of use, it's always been at 7500 mile intervals as far as I can tell. That doesn't mean it couldn't, or even doesn't, sense things like cold operating time, etc.

The oil level sensor is a float which drives a couple of magnetic reeds for mine. The original float got "oil-logged" and falsely indicated low oil when it was hot.

Cheers, Tom

It would be helpful if we knew the make, model, and year of the vehicle.

In article , 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?

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

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.

I am not sure you are giving them enough credit stu. I don't claim to be the almighty expert either. I think they measure operating hours, crank revolutions and operating temperatures at a minimum and calculate useable oil life from that data.

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.

In article , 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.

Last May I put 12,000 miles on my bike, driving about 10 hours a day averaging 3200 rpm. That would have be about

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.

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.