oil changing frequency - questioning the gospel

[Jon Tara <jtara@xxxxxxxxxxxxxx>]

MUDSCOW@domain.elided asked how bad the oil is at 3K, 4K, 5K, 10K, etc.

One (and, really the only) way to find out is to have your oil tested.
It's (relatively) cheap, fun, and prudent.

I had mine tested by the fellow who sells me my Red Line. He uses suction
device to take a sample of oil through the dipstick while the engine is
running. He collected $35, and sent it off to the lab (Analysts, Inc. 2910
Ford Street, Oakland CA, 94601-2821, (800) 424-0099) and I got a report
back in about a week.

They will keep your records on file, and will report on trends when you
re-test.

There are a number of tests that are possible, but here's what I got:

1) Spectrochemical analysis of Various metals - can tell you about
specific maintainence problems.

2) SAE grade, total solids, fuel %, water %

3) TAN (total acid number) TBN (total base number)

I'm told that the things you really want to watch to determine when to
change the oil are TAN and TBN. These tell you when the additive packet is
used-up.

I had mine tested with 3800 miles on the oil, and 60,000 miles on the
engine. TAN was 1.85 (good), TBN 8.02 (new oil is 12, 2.0 is considered 
minimum, and oil needs to be changed then).

To give you an idea what they report on, here are my spectro
numbers:  (metals that could indicate wear problems follow) 8ppm iron, <1 
chromium, 9ppm aluminum, 14 lead, 15 copper, 9ppm tin, <.1ppm silver, 
<1ppm titanium, 13ppm silicon, 2ppm boron, (I think the following are all 
oil additives)) <10ppm potasium, 807ppm molybdenum, 1467ppm zinc 
(molybdenum and zinc are added by RedLine as anti-scuffing agents), 1376 
ppm phosphorus, 3156ppm calcium, <10ppm barium, 
457ppm magnesium, <10ppm antimony, <1ppm vanadium (fuel contaminant).

They will "flag" excessive numbers (none were flagged) and provide a handy
guide that what specific metals may indicate. 

Other numbers reported were ,0.5% fuel, 0.1% total solids, <0.05% water,
Vis 16.0, SAE grade 40, TAN 1.85, TBN 8.02.

Based on the report, my oil dealer suggested a 5-6K change interval.

I plan on re-testing every 6 months or so, as much for my education as for
preventative mantainence.

- -----
Jon Tara
95 325is
and know EXACTLY what's in it's oil :)

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