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Daddy-O
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Discussion Starter · #1 ·
Hi,

Is anyone familiar with the algorithm used by the on board computer to figure out the next oil change?

I average about 10 trips to work each week at 4 miles per trip, though it takes about 15 minutes in traffic. Plus one trip of maybe 15 miles each way. Plus a few other in-town trips maybe.

My current computer reading is to have it changed in 4k miles, which would be about 8k after the last change.

I'm wondering if it really does account for short trips where the oil may not heat up all the way or just fuel consumption or ?

Thanx,
M
 

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2015 335 M-Sport Mineral Gray
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I just got my oil change at 12,200 miles per the SI on Friday. (My first oil change was at 7,000 miles but the SI was not reset)

Last Monday my SI said I had 200 miles to go. Wednesday afternoon it said I was down to 0 miles although I had only driven less than 45 miles in those 3 days. :confused: My commute is 4.5 miles each way, mostly freeway going to work, but all surface roads coming back.

When I got the car back it said the Inspection I is scheduled in 15,500 miles. I have already knocked a couple hundred miles of that.
 

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My TARDIS is a BMW
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5,352 Posts
redbeemer said:
The onboard computer doesn't just use distance driven?
Distance driven isn't the best indicator or how "hard" the oil has been worked. If two cars are driven the same total distance, but car A does it by taking many many many very short trips and car B does it by taking fewer but longer trips, the oil in car A has been abused more than in car B. In this case, car A would have much worse gas mileage than car B, and BMW figured out that oil lifetime is better correlated to the average gas mileage (and thus number of tanks of gas) than it is to total distance travelled.
 

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Premium Member
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I don't know the exact numbers, but each green bar represents something on the order of 1000 liters of fuel used or about 260 gallons. I don't think I have the number exactly correct but it is in the ballpark....

Our tanks are 18.5 gallons (E39/60 for sure) and the average fuel up, I'm guessing, is around 16-17 gallons so that is like 16 visits to the pumps. Figure a HIGH average fill up of once a week so that is 16 weeks to burn one green bar and 64 weeks to burn through all 4 to hit the yellow bar. That isn't too far off of 1 year and I'm mostly guessing at these numbers.
 

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Daddy-O
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307 Posts
Discussion Starter · #7 ·
What happens to oil???

So, what happens to oil exactly when you do lots of short trips compared to less long trips of equal mileage?

I heard that if you don't heat up the engine that any water moisture in the engine doesn't burn off. Is that the primary culprit?
 

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My TARDIS is a BMW
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2b9m3w said:
So, what happens to oil exactly when you do lots of short trips compared to less long trips of equal mileage?

I heard that if you don't heat up the engine that any water moisture in the engine doesn't burn off. Is that the primary culprit?
Pretty much. You end up with a nice frothy oil/water mixture, which isn't a very good lubricator.
 

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M Mad
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10,476 Posts
Also when the engine is cold, you get more blow by in the cylinders and thus mroe combustion products in the oil.

Also cold oil is subjected to more shear stresses, leading to lower viscosity.

Older algorithms included number of cold starts, but fuel consumption does it for you.
 

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ey

Pinecone said:
Also when the engine is cold, you get more blow by in the cylinders and thus mroe combustion products in the oil.

Also cold oil is subjected to more shear stresses, leading to lower viscosity.

Older algorithms included number of cold starts, but fuel consumption does it for you.
i travel 80 miles a day everyday goin to work..i work 5 days a week from woodlandhills to commerce 101 to the 5. is this bad for my beemer 328i?shud i consider getting another car like just working car?in the morning is cruising but goin home is somtimes stop and go cos of trafiic. i used up almost 5000 miles in two montsh?any advice?
 

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Premium Member
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If I recall correctly I think Pete T posted that the OBC uses 601 gallons of fuel as the consumed unit to count down to the service interval.

I'm about 50 miles from my first one, and using current mileage and 601 gallons, the average MPG reading is right on.

Search for "601 gallons" -- I am on travel and on dial up ( :eeps: ) this week...
 

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Daddy-O
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Discussion Starter · #12 ·
Thanks for the replies guys! It definitely makes sense.

I was also thinking about how stop-and-go driving could adversely affect your car (even if the engine gets hot enough to avoid the oil/water problem and blowby).

I would guess stop-and-go driving just puts more stress on everything since there is more acceleration. I.e. pistons are changing velocity abruptly, and since F=ma there are more forces at work... Of course ditto for all the other car parts like suspension etc.
 

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The King of Common Sense
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2b9m3w said:
Hi,

Is anyone familiar with the algorithm used by the on board computer to figure out the next oil change?

I average about 10 trips to work each week at 4 miles per trip, though it takes about 15 minutes in traffic. Plus one trip of maybe 15 miles each way. Plus a few other in-town trips maybe.

My current computer reading is to have it changed in 4k miles, which would be about 8k after the last change.

I'm wondering if it really does account for short trips where the oil may not heat up all the way or just fuel consumption or ?

Thanx,
M
The correct number is 667 gallons of gas. That equates to 22.49 mpg average over 15,000 miles.

http://bimmer.roadfly.org/bmw/forums/e46/121712-1.html

Author: Dave 330i 5spd SP on 2001-11-11 at 23:24:50
Message: The OBC does not know when you changed your oil. Have it reset when the dealer gives you are first 15K service. Do not have the service indicator reset when you change oil between the 15K services.

BTW, the way the-time-to-service indicator works is when 667 gallons of gasoline is consummed then it is time to change your oil.
 

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M Mad
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Highway cruising is the least stressful on teh car and oil in general.

Stop and go is not good, cold starts are not good, high power settings is not good, hard acceleration is not good.

As to getting another car, I would say then you would be commutingin a pos, and why would you want to do that? :) Drive your BMW and enjoy the experience.
 
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