An Oil Change Odessy

[shendrick]

The M3 was purchased in 12/08. I do a litlte under 1K miles/month. The 1200 mile oil change was done in 2/09 and most posting on the forum suggest doing oil changes every 7500 or so. The Stealer in my area quoted me over $300 for an off cycle oil/filter change so I decided to do it myself. Did it in 12/09 at about 11,000 miles (due to procrastination) but only put 8.5L in since better to underfill and then top off instead of having to drain some out.

The sensor said I was down 1/4 liter after my oil/filter change. This reading did not change for days, so after a week I added another .25L. I then waited about 10 days during which the sensor said I was still down .25L. So, I added another .25L and drove my 10 miles to work during at which time the sensor said I was still down .25L. This reading by the way was not not an on-demand reading by me, but simply a reading the car displayed after the oil warmed up. I bought gas before just before parking at the office during which time I did an on-demand reset of the oil indicator. You all know what happened, > Max. So I want home, put it up on the ramps and drained the front sump which contained about .25L (althougth I did not measure accurately). After restarting the car (without an on demand oil reset) the display said > max. I then did an on-demand oil reset and got a 100% reading. I repeated this several time with the same results.

There are 3 key take aways from this odessy.

1. The oil level sensor does not seem to reasd very accurately when left on its own.
2. The oil level sensor is not that accurate, hence BMW's instructions not to add oil except in .5L increments.
3. I resused the old crush washer when draining the front sump. Does anyone know if this is a really bad or not so bad idea.

[ideliver]

Getting the hang of the e-dipstick takes some time...read you manual carefully concerning its function...it doesn't work the way you were thinking it worked...

As far as the crush washer goes....you should be okay, it would have leaked by now...

Just make sure that you don't overtighen the drain plugs...I use a torque wrench...if you strip that bolt you are in for big hassle...

[Dartanium]

what's an on demand oil reset? I would like to know the procedures should I decided to do an oil change in between service, thanks.

[shendrick]

This is my terminology. When you rotate through the various information displays on the dash (not the nav system window) oil level is one of the displays. When I changed the oil, I leave the car displaying the oil level so I could monitor whether I put enough in.

Here's the weird part. The car obviously refreshes this information each time you start it after it warms up. I always figured that this was no different from depressing the button on the left stalk and holding it to force the car to recalculate the oil level "on demand" (as in the driver asking for a refreshed reading). After I changed the oil in the car it continued to say I was .25L low - which made sense to me since I put 8.5L in. Hence my efforts to correct over time by adding first .25L, waiting a number of days watching the display after the car warmed up, and then ultimately another .25L. After the 2nd addition of .25L, the car showed the same reading of being down .25L after 10 miles of driving. I then did an on-demand refresh of the oil level and got >max.

I can't believe that the car does any sophisticated averaging in its oil calaculation or that this differs from what happens when the driver asks for this information to be refreshed on-demand. So I infer that the differences being the crappy accuracy of of the oil sensor. I know the manual says not to add less than .5L, but it bugs me to always be driving the car with a little less oil than I should.

[JCtx]

Originally Posted by shendrick

1. The oil level sensor does not seem to reasd very accurately when left on its own.
2. The oil level sensor is not that accurate, hence BMW's instructions not to add oil except in .5L increments.
3. I resused the old crush washer when draining the front sump. Does anyone know if this is a really bad or not so bad idea.

Finally somebody else who took the time to 'understand' the sensor . When left on its own, sensor will take a reading randomly, most likely when engine is NOT idling, plus you can be braking, negotiating a curve, etc., so it'll NEVER be consistent that way.

Few comments. Sensor is consistent; just remember it's a sensor, which means you can be in-between probes and reading will be the same. Notice I didn't say 'accurate', since its accuracy is only 1/4 of a liter, but once you understand how it works (like you did), we can make it relatively accurate as well . When you added the first .25L, you were a hair below full, but you didn't know, hence the 3/4 level still displayed. Remember your initial 3/4 level could have been very close to 3/4 or just above 1/2, meaning you have a possible variance of 1/4-lt; does that make sense? Once you understand that, you can easily top off your oil from now on without drama. Yes, next time just add a tad of oil at a time after the first 1/4-lt, wait until it registers full, and you'd be perfect. By the way, if you check your oil level regularly, when sensor first drops to 3/4, it means you'd be a tad over 1/4-lt short (remember oil level should be BELOW the 3/4 level probe to register 3/4, rather than full), so just add a tad over 1/4 initially, and a tad more at a time if needed.

I always keep oil topped off on all my vehicles. Waiting for the '+1L or risk engine failure' is crazy IMO (especially with oil not available anywhere but dealers), but we're in the minority . Having to carry a liter in the trunk, like a 20-yr-old clunker, is ridiculous too (no need to do that when topped off).

As far as 'on demand', that's a great term to avoid the confusion. I've said many times that sensor is useless unless done 'on demand', and with a few conditions you didn't mention: use always same FLAT spot (garage is best), always do it after driving at least 15 miles (takes less than a minute that way, and it's pretty consistent), and at idle, obviously. That way you'd always be doing it under the SAME conditions.

Finally, you can reuse crush washers many times, but when doing so, always smooth them with fine sandpaper to avoid having to overtighten the drain bolt to avoid a leak . Great post man. Your new term might encourage some more folks to NOT be afraid of a darn sensor . Good day.